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PubMedDate not supplied

[Epidemiology of identical twin pregnancy].

On the basis of MEDLINE and manual search, we looked at the main papers in English literature published from 1976, regarding risk factors for spontaneous (i.e. not related to fertility drug use) multiple births. The constant frequency of monozygotic (MZ) pregnancies over time and in different geographic areas suggests that determinants of MZ twins are largely unchanged over time and that genetic mechanism may act a role. On the contrary, temporal and geographic trends observed in dizygotic (DZ) pregnancies suggest that environmental factors play a role in determining this condition. At present maternal age and hereditary components are the better defined determinants for spontaneous multiple births.

Female↗
PubMed2000

Risk factors for intraventricular hemorrhage in a birth cohort of 3721 premature infants.

AIMS: In our study we determined possible risk factors for intraventricular hemorrhage grade III to IV (IVH) based on a regional German neonatal data base and tried to build a logistic-regression model to predict the risk of IVH according to gestational age. MATERIALS: We identified 3721 premature infants, 22 to 36 completed weeks of gestational age, born from 1994 through 1997. 136 (3.7%) IVH were diagnosed sonographically. 60 (44%) infants with IVH died. We examined the following variables as risk factors for IVH: gestational age, sex, blood pH of 7.2 or less, body temperature of 35 degrees C or less, multiple birth, small-for-gestational age, intubation after birth, transport to another hospital. RESULTS: In the full logistic regression model sex, blood pH of 7.2 or less, multiple birth, and small-for-gestational age were not associated with a significant risk of IVH. Body temperature of 35 degrees C or less was associated with an increased risk of IVH (adjusted odds ratio, 1.92; 95% confidence interval, 1.09 to 3.40). Intubation after birth increased the risk of IVH in neonates under 28 weeks of gestational age (OR, 3.72; 95% CI, 1.65 to 8.38) only to a moderate extent, but significantly in neonates 32 to 36 weeks of gestational age (OR, 16.51; 95% CI: 7.35 to 36.18). The risk of IVH was mainly related to gestational age. Neonates delivered before 28 weeks of gestation (OR, 75.72; 95% CI, 46.14 to 124.30) faced the highest risk of IVH. Transport to another hospital was connected with an increased risk of IVH regardless of gestational age (adjusted OR, 1.95; 95% CI, 1.07 to 2.56). CONCLUSION: The frequency of IVH could be reduced significantly, if extremely premature infants, the vast majority of patients suffering from IVH, did not have to be transferred postnatally to another hospital.

Birth Weight↗
PubMedDate not supplied

What do women know about the risks of delayed childbearing?

BACKGROUND: Women aged 35 and older account for an increasing proportion of births and are at increased risk of pregnancy complications and poor infant outcomes. The objectives of the study were: 1) to determine what women know about delayed childbearing, including pregnancy complications and outcomes associated with low birthweight (LBW, < 2500 grams), preterm delivery (< 37 weeks) and multiple birth, and 2) to assess the characteristics of women with limited knowledge of risks. METHODS: A computer-assisted telephone interview survey was conducted with 1,044 randomly selected women who delivered their first live-born infant, between July 2002 and September 2003, in two urban centres, Calgary and Edmonton, in Alberta, Canada. RESULTS: The proportion of women aware of specific childbearing risks associated with advanced maternal age were as follows: conception difficulties (85.3%), multiple birth (24.0%), caesarean section (18.8%), preterm delivery (21.8%), and LBW (11.2%). Knowledge of specific developmental and health-related risks of suboptimal infant outcomes ranged between 18.0% and 46.5%. Logistic regression revealed that limited knowledge of maternal age-related pregnancy risks were associated with unplanned pregnancy (OR, 1.48; 95% CI, 1.03-2.14), smoking (OR, 1.83; 95% CI, 1.29-2.60) and non-use of fertility treatment (OR, 2.15; 95% CI, 1.44-3.19). Characteristics associated with limited knowledge of the risks associated with suboptimal birth outcomes were: age 35-39 years (OR, 2.98; 95% CI, 1.35-6.58), less than post-graduate education (< or = high school OR, 2.14; 95% CI, 1.20-3.82), and not currently enrolled as a student (OR, 1.75; 95% CI, 1.02-3.00). CONCLUSIONS: Many women are generally unaware of the potential consequences of delayed childbearing. There are missed opportunities in preconception counselling and education, which should be addressed to allow for more informed decision-making about family planning.

Adult↗
PubMed1998

The changing pattern of prenatal care utilization in the United States, 1981-1995, using different prenatal care indices.

CONTEXT: Two measures traditionally used to examine adequacy of prenatal care indicate that prenatal care utilization remained unchanged through the 1980s and only began to rise slightly in the 1990s. In recent years, new measures have been developed that include a category for women who receive more than the recommended amount of care (intensive utilization). OBJECTIVE: To compare the older and newer indices in the monitoring of prenatal care trends in the United States from 1981 to 1995, for the overall population and for selected subpopulations. Second, to examine factors associated with receiving intensive utilization. DESIGN: Cross-sectional and trend analysis of national birth records. SETTING: The United States. SUBJECTS: All live births between 1981 and 1995 (N=54 million). MAIN OUTCOME MEASURES: Trends in prenatal care utilization, according to 4 indices (the older indices: the Institute of Medicine Index and the trimester that care began, and the newer indices: the R-GINDEX and the Adequacy of Prenatal Care Utilization Index). Multiple logistic regression was used to assess the risk of intensive prenatal care use in 1981 and 1995. RESULTS: The newer indices showed a steadily increasing trend toward more prenatal care use throughout the study period (R-GINDEX, intensive or adequate use, 32.7% in 1981 to 47.1 % in 1995; the Adequacy of Prenatal Care Utilization Index, intensive use, 18.4% in 1981 to 28.8% in 1995), especially for intensive utilization. Women having a multiple birth were much more likely to have had intensive utilization in 1995 compared with 1981 (R-GINDEX, 22.8% vs 8.5%). Teenagers were more likely to begin care later than adults, but similar proportions of teens and adults had intensive utilization. Intensive use among low-risk women also increased steadily each year. Factors associated with a greater likelihood of receiving intensive use in 1981 and 1995 were having a multiple birth, primiparity, being married, and maternal age of 35 years or older. CONCLUSIONS: The proportion of women who began care early and received at least the recommended number of visits increased between 1981 and 1995. This change was undetected by more traditional prenatal care indices. These increases have cost and practice implications and suggest a paradox since previous studies have shown that rates of preterm delivery and low birth weight did not improve during this time.

Adolescent↗
PubMed1991

Randomized, placebo-controlled trial of human surfactant given at birth versus rescue administration in very low birth weight infants with lung immaturity.

A randomized, placebo-controlled trial of human surfactant given intratracheally at birth (prophylactic) versus rescue administration after the onset of severe respiratory distress syndrome (RDS) was conducted among preterm infants born at 24 to 29 weeks of gestation. Singleton fetuses were randomly assigned to receive (1) placebo (air), (2) prophylactic surfactant treatment, or (3) rescue surfactant treatment; infants of multiple births received either (1) prophylactic or (2) rescue treatment. Of 282 potentially eligible fetuses, 246 infants received treatments at birth and 200 infants had RDS. Outcomes are presented both as an intention-to-treat analysis (including infants who met exclusion criteria at or after birth) and as a full treatment protocol analysis for those infants with RDS and likely to benefit from surfactant. Preterm infants (mean 1.0 kg birth weight, 27 to 28 weeks of gestational age) randomly assigned to receive prophylactic treatment received surfactant soon after birth; those assigned to receive rescue surfactant had instillation at a mean age of 220 minutes if the lecithin-sphingomyelin ratio was less than or equal to 2.0 and no phosphatidylglycerol was detected in either amniotic fluid or initial airway aspirate, oxygen requirements were a fraction of inspired oxygen of greater than 0.5, and mean airway pressure was greater than or equal to 7 cm H2O from 2 to 12 hours after birth. Up to four treatment doses (or air) were permitted within 48 hours; approximately 60% of surfactant-treated infants required two or more doses. Surfactant-treated infants had significantly less pulmonary interstitial emphysema than placebo-treated infants (p = 0.02), but there were no other significant differences in mortality rates or morbidity. Indexes of oxygenation and ventilation were improved in surfactant recipients during the first 24 hours. An intention-to-treat analysis found no significant differences between infants given placebo and surfactant-treated infants or between prophylactic- and rescue-treated infants; an improved total mortality rate (p = 0.002) was found among surfactant-treated infants in Helsinki but not in San Diego. Among infants with RDS, the total mortality rate was significantly improved (p = 0.004) with surfactant treatment but not the proportion alive and without bronchopulmonary dysplasia at 28 days (p = 0.052), or the proportion alive and without bronchopulmonary dysplasia at 38 weeks of postconceptional age (p = 0.18) to adjust for differences in prematurity. Deaths caused by RDS or bronchopulmonary dysplasia were significantly reduced among surfactant recipients (p = 0.0001). Neither among singletons nor among multiple-birth infants was there a selective advantage to prophylactic versus rescue treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Bronchopulmonary Dysplasia↗
PubMed1995

Retinopathy of prematurity in a south Australian neonatal intensive care unit.

PURPOSE: To establish the incidence and severity of retinopathy of prematurity (ROP) in an Australian population of premature infants, and define risk factors for this population. METHODS: A survey of neonates born weighing less than 1501 g and/or with gestational age below 33 weeks, was undertaken at a neonatal intensive care unit in South Australia. RESULTS: ROP was diagnosed in 16.0% of the 94 neonates who were screened until retinal vascularisation was complete. Threshold disease occurred in 4.2%. Logistic regression identified three significant risk factors for the development of ROP: days of mechanical ventilation, multiple birth and female sex. CONCLUSIONS: The incidence of ROP was relatively low when compared with figures recently published for two large populations studied in the United States and England. This difference was due to a lower incidence of mild forms of the disease. Days of mechanical ventilation, multiple birth and female sex were independently predictive of the occurrence of ROP. As small numbers of infants with ROP are managed at individual Australian centres each year, a national ROP register is recommended to facilitate the study of the disease in this country.

Female↗
PubMedDate not supplied

[Reproductive medicine in Germany--peculiarities and dilemmas].

BACKGROUND: Technological progress, as well as increasing success, of reproductive medicine may lower the threshold for childless couples to initiate infertility therapy. However this development may aggravate unsolved problems (e. g. multiple births) and may not increase the pregnancy rate, due to the present unsatisfactory legal situation in Germany (e. g. ban on selective blastocyst culture). METHODS: Based on a systematic review of the literature, we studied actual problems of German reproductive medicine under three public health-related topics: (1) the decline in population in Germany, (2) criteria for success in reproductive medicine and (3) new treatment options in the light of legal and ethical aspects. RESULTS: In Germany (and other industrial nations), reproductive medicine has emerged parallel to an ever-increasing rate of childlessness. Today, 2 % of all births result from treatments using the techniques of reproductive medicine. Nevertheless, the actual extent of involuntary childlessness is lower (below 8 %) than commonly suggested (between 10 and 15 %). Frequently, the success of treatment depends upon a series of treatment cycles and is, especially in Germany, accompanied by a high rate of multiple births (more than 30 %). Hence, a more adequate success rate may be the healthy, i. e., term, singleton baby. The use of selective blastocyst culture, currently not permitted in Germany, could further improve therapy or, at least, reduce patient stress and discomfort. CONCLUSION: Reproductive medicine, as seen from a public health perspective, needs to pursue patient-oriented requirements more in-depth. An open discussion of new technologies which could improve reproductive health but are at present not permitted, would be imperative.

Germany↗
PubMed1983

Cancer in mothers of dizygotic twins.

For the determination of whether mothers of dizygous (DZ) male-female twins or other polyzygous (unlike sexed) multiple births have cancer incidence different from that of controls, a cohort study was conducted with the use of the records of the Connecticut Twin Registry and the Connecticut Tumor Registry (CTR). A total of 3,982 women born between 1885 and 1935 who had borne DZ (male-female) twins or who had experienced other polyzygous multiple births in Connecticut during 1925-59 and a control group of 3,982 women, matched pairwise on year of childbirth, age, number of previous children, race, and national origin, were searched in the CTR for the incidence of cancer of all sites. Women who have DZ twins have a higher level of gonadotropins than women in the general population. A hypothesis that mothers of DZ twins may have a higher incidence of breast cancers than other women was investigated; the results did not support the hypothesis. There was, however, an excess incidence of cancer of the pancreas among mothers of twins. The relative risk was 3.2 (P = 0.026, exact two-tail probability) with exact 95% confidence limits (1.12, 11.16). These results are consistent with findings from autopsy data which suggested that among women but not among men with pancreatic duct cell carcinoma, there is excessive gonadotropic activity. These results are also consistent with early findings of high follicle-stimulating hormone (FSH) in the urine of diabetics and high FSH in the urine of postmenopausal women.

Adult↗
PubMed2003

Cord blood red cell osmotic fragility: a comparison between preterm and full-term newborn infants.

BACKGROUND: The osmotic fragility of red blood cells reflects their membrane ability to maintain structural integrity. The osmolality at which the cells lyse is related to their shape, deformability, surface area/volume ratio and intrinsic membrane properties. In cord blood, there may be differences between premature and term infants, and be influenced by maternal medication and other factors. There have been no definitive findings on possible differences between preterm and full-term infant osmotic fragility. AIMS: To determine if cord blood erythrocyte osmotic fragility differs between premature and full-term newborn infants, using two parallel techniques. PATIENTS AND METHODS: Cord blood samples were obtained from preterm singletons (N=11), preterm multiple births (N=10), full-term infants (N=24), as well as adults (N=22), for comparison. An osmotic fragility test was used to determine the NaCl concentration at which 20%, 50% and 80% of hemolysis occurred using individual logistic curves. A glycerol lysis test determined the time needed to lyse 50% of red blood cells. RESULTS: Cord blood red cells of multiple birth premature infants were more hemolysis-resistant than erythrocytes from full-term infants or adults. Another index of osmotic fragility, the difference in NaCl concentration for 80% and 20% red cell hemolysis showed that premature infants had greater differences than full-term infants or adults. Glycerol lysis time revealed that both preterm and full-term infants had an erythrocyte subpopulation that took longer than adult blood to attain 50% hemolysis. Correlation between both tests was very significant (r=-0.603, P<0.0001, N=67). CONCLUSIONS: This study shows that erythrocytes of premature infants, although, in average, less osmotically fragile than those of healthy full-term infants, contain a more hemolysis-susceptible cell subpopulation.

Adult↗
PubMed2001

[Preliminary study on application of blastocyst culture and day 5 transfer in patients with low oocyte number].

OBJECTIVE: To evaluate whether blastocyst culture and transfer in patients with low oocyte number can effectively improve the outcome of in vitro fertilization-embryo transfer treatment. METHODS: Retrospectively analyze 59 couples received conventional in vitro fertilization and embryo transfer (IVF-ET) treatment in our center from January to February 2000. Twenty-one couples had blastocyst culture and day 5 embryo transfer and another 38 couples had day 2 embryo transfer as the control. Their clinical and laboratory results were compared between these two groups. RESULTS: In day 5 group the mean oocytes retrieved were (6.6 +/- 2.8), the clinical pregnancy rates (PRs) was 43% and the life delivery rate was 38%; while in day 2 group the results were (6.9 +/- 3.7), 37% and 29% respectively. There was no significant difference between two groups. No high-order multiple birth occurred in day 5 group, but in day 2 group there were two cases: one with triplets and another with pentadriplet who had the embryos reduction. CONCLUSIONS: These results demonstrate that nonselective blastocyst culture and transfer in patients with low oocyte number seems not effectively to improve the PRs and the delivery rate, but may decrease the occurrence of multiple birth without affecting the final pregnancy results when compared with conventional day 2 transfer.

Blastocyst↗
PubMed1991

[Epidemiology and morphology of sudden death in infancy in twins and siblings].

429 SIDS cases were investigated in a retrospective study. For this study, the deaths in which at least one brother or sister had died under comparable circumstances were evaluated. The 429 babies who had died comprised 17 multiple birth babies (3.7%) including 15 twin and two triplet babies. Eleven cases (2.6%) were brothers or sisters of SIDS victims. In three cases, relatives of the baby's mother had died of sudden infant death. A comparison of the various case groups did not reveal any patho-morphologically significant differences between the groups or differences from other SIDS cases. All the multiple birth babies were immature and premature babies. There was a raised incidence of poor socio-economic conditions in the sibling group. The results are significant for parent counselling, any preventive measures and the detection of concurrent (in particular, unnatural) causes of death.

Autopsy↗
PubMed2006

The Scottish Perinatal Neuropathology Study--clinicopathological correlation in stillbirths.

OBJECTIVE: To examine the neuropathology of fetuses dying before birth, to determine the timing of any brain damage seen and to ascertain clinical associations of pre-existing brain damage. DESIGN: Population-based observational study. SETTING: All 22 delivery units within Scotland, 1995-1998. SAMPLE: All stillborn fetuses > or =24 weeks of gestation excluding those with chromosomal abnormality or central nervous system/cardiothoracic malformation. METHODS: Clinical detail was collected on all stillborn fetuses. Requests for postmortem included separate request for detailed neuropathological examination. Stillborn fetuses were classified as full term antepartum (normal growth/growth restricted), preterm antepartum (normal growth/growth restricted), intrapartum (full term/preterm), multiple births and stillborn fetuses following abruptions. Clinicopathological correlation attempted to define the timing of brain insult. Placentas were examined for each case where available. MAIN OUTCOME MEASURES: Presence of established and/or recent brain damage. RESULTS Clinical details were available for 471 stillborn fetuses, and detailed neuropathology was possible in 191 cases. Of these 191, 13 were multiple births, 9 died following abruption, 12 were intrapartum deaths and 157 were antepartum stillborn fetuses (99 preterm and 58 full term). Recent or established brain damage was seen in 66% of the entire cohort. Thirty-five percent of all cases showed well-established hypoxic damage predating the last evidence of fetal life, and this was more common in preterm fetuses (P = 0.015), those fetuses with evidence of recent damage (P < 0.001), in pregnancies complicated by pregnancy-induced hypertension (P = 0.044) and those in whom the placenta was <10th centile (P = 0.002). CONCLUSIONS: Brain damage is commonly seen in stillborn infants, and in around one-third of cases, damage predates the period immediately before death. Factors suggesting suboptimal placental function are associated with such damage. Early identification of placental impairment may lead to improved pregnancy outcome.

Abruptio Placentae↗
PubMed2003

Triplets and quadruplets in Switzerland: comparison with singletons, and evolution over the last decade.

AIMS: Main objectives were 1) to determine the incidence of higher multiple births from 1995 to 1998 in Switzerland, and 2) to evaluate neonatal mortality and morbidity. Secondary objectives were 3) to compare the results with those of matched singletons, and 4) to compare the present data to the first Swiss study (1985-1988). METHODS: Retrospective analysis of maternal and neonatal data obtained from all Swiss hospitals. RESULTS: The incidence of triplet births was 1/3247 and that of quadruplet births 1/81,186. The median gestational age was 32 5/7 weeks for triplets, and 28 6/7 weeks for quadruplets. The median birth weight was 1665 g for triplets and 1076 g for quadruplets. Perinatal mortality was 6% for triplets and 19% for quadruplets. Respiratory distress syndrome was the major morbidity as diagnosed in 52% of triplets and 81% of quadruplets. A comparison of triplets with matched singletons showed no significant differences in morbidity and mortality. Compared with the first Swiss study, the mortality rate decreased, while the incidence of triplets increased but decreased for quadruplets. CONCLUSION: The incidence of higher-order multiple births in Switzerland dropped for quadruplets in the last decade but has increased for triplets. The mortality and morbidity of triplets is comparable to that of singletons with a similar gestational age.

Cesarean Section↗
PubMed2002

Is hemifacial microsomia linked to multiple maternities?

Hemifacial microsomia describes a congenital orofacial malformation in which there is insufficient or disrupted development of the mandible affecting one side of the face. The aetiology of this condition remains unclear, but it has been postulated that twins (predominantly monozygotic) are more liable to be affected than singletons. This study investigates the incidence of multiple births amongst a large number of affected individuals and their families. Data were collected on 145 individuals with hemifacial microsomia and microtia, using postal questionnaires and interviews in a hospital setting. These data were compared with the mean age-standardised twin maternity prevalence for England and Wales between 1975 and 1995 of 1.06% and the triplet maternity prevalence for England and Wales for 1995 of 0.034% (a multiple maternity being where more than one baby is born, either alive or stillborn). The prevalence of twin maternities amongst the affected individuals was 3.96% (P>0.05) and amongst their siblings it was 4.02% (P<0.02). There was also an excess of twins in the rest of the family groups, predominantly due to a stronger history of twinning on the maternal side. As there were more twins amongst the affected individuals than in the general population, it seems likely that whatever the aetiology of hemifacial microsomia and microtia, the presence of a co-twin (or co-triplets) may make the causal event, or series of causal events, more likely to occur. This study supports the hypothesis that hemifacial microsomia and microtia are in some way linked to multiple births. Analysis of this link may provide new directions for research into the aetiology of a variety of congenital defects.

Diseases in Twins↗
PubMed2006

Patient misidentification in the neonatal intensive care unit: quantification of risk.

OBJECTIVE: To quantify the potential for misidentification among NICU patients resulting from similarities in patient names or hospital medical record numbers (MRNs). METHODS: A listing of all patients who received care in 1 NICU during 1 calendar year was obtained from the unit's electronic medical record system. A patient day was considered at risk for misidentification when the index patient shared a surname, similar-sounding surname, or similar MRN with another patient who was cared for in the NICU on that day. RESULTS: During the 1-year study period, 12186 days of patient care were provided to 1260 patients. The unit's average daily census was 33.4; the maximum census was 48. Not a single day was free of risk for patient misidentification. The mean number of patients who were at risk on any given day was 17 (range: 5-35), representing just over 50% of the average daily census. During the entire calendar year, the risk ranged from 20.6% to a high of 72.9% of the average daily census. The most common causes of misidentification risk were similar-appearing MRNs (44% of patient days). Identical surnames were present in 34% of patient days, and similar-sounding names were present in 9.7% of days. Twins and triplets contributed one third of patient days in the NICU. After these multiple births were excluded from analysis, 26.3% of patient days remained at risk for misidentification. Among singletons, the contribution to misidentification risk of similar-sounding surnames was relatively unchanged (9.1% of patient days), whereas that of similar MRNs and identical surnames decreased (17.6% and 1.0%, respectively). CONCLUSIONS: NICU patients are frequently at risk for misidentification errors as a result of similarities in standard identifiers. This risk persists even after exclusion of multiple births and is substantially higher than has been reported in other hospitalized populations.

Humans↗
PubMed2004

The National Women's Health Study: assembly and description of a population-based reproductive cohort.

BACKGROUND: Miscarriage is a common event but is remarkably difficult to measure in epidemiological studies. Few large-scale population-based studies have been conducted in the UK. METHODS: This was a population-based two-stage postal survey of reproductive histories of adult women living in the United Kingdom in 2001, sampled from the electronic electoral roll. In Stage 1 a short "screening" questionnaire was sent to over 60,000 randomly selected women in order to identify those aged 55 and under who had ever been pregnant or ever attempted to achieve a pregnancy, from whom a brief reproductive history was requested. Stage 2 involved a more lengthy questionnaire requesting detailed information on every pregnancy (and fertility problems), and questions relating to socio-demographic, behavioural and other factors for the most recent pregnancy in order to examine risk factors for miscarriage. Data on stillbirth, multiple birth and maternal age are compared to national data in order to assess response bias. RESULTS: The response rate was 49% for Stage 1 and 73% for the more targeted Stage 2. A total of 26,050 questionnaires were returned in Stage 1. Of the 17,748 women who were eligible on the grounds of age, 27% reported that they had never been pregnant and had never attempted to conceive a child. The remaining 13,035 women reported a total of 30,661 pregnancies. Comparison of key reproductive indicators (stillbirth and multiple birth rates and maternal age at first birth) with national statistics showed that the data look remarkably similar to the general population. CONCLUSIONS: This study has enabled the assembly of a large population-based dataset of women's reproductive histories which appears unbiased compared to the general UK population and which will enable investigation of hard-to-measure outcomes such as miscarriage and infertility.

Abortion, Spontaneous↗
PubMed2003

Towards single births after assisted reproduction treatment.

The cause of increases in recorded multiple births is undoubtedly assisted human conception. Many arise when three or more embryos are replaced after IVF or ISCI. Others are due to multi-ovulation during artificial insemination or intrauterine inseminations, since complete control over numbers of ovulated eggs following ovarian stimulation is not fully possible. The frequency of multiple IVF births is best controlled by reducing numbers of transferred embryos to one or two. Methods to induce ovarian stimulation in amenorrhoeic and then in cyclic women 30 years ago have been greatly refined and extended in current practice. Curiously, a great many of them produce oocytes which fail to implant after fertilization, whether natural or induced cycles are being used. This massive failure of most embryos to implant poses numerous questions on the evolution of this situation in humans.

Animals↗
PubMed1985

Overripe ova and twinning.

Multiple births were studied in a sample of orthodox Jewesses for whom an estimate could be made of the day of ovulation and the earliest possible day of conception. The overall rate of twinning was 14.5/1,000 deliveries, and of triplets, 0.40/1,000. Twinning rates varied significantly from 11.4 in the 5,976 "early" conceptions (day -1 or earlier relative to the estimated day of ovulation) to 26.9 in the 1,498 "late" conceptions (day 0 or later). Triplets varied significantly from 0 to 2.01 in early and late conceptions, respectively, and unlike-sexed multiple sets, 2.8 and 12.8, respectively. The excess of multiple births in late conceptions was seen within different ages and origin groups, in women with different menstrual characteristics, and in those with and without treatment for anovulation. While the excess of unlike-sexed sets seems to lead to the conclusion that late conceptions are associated with dizygosity, polar body twinning and uniovular dispermatic twinning should also be considered.

Adult↗