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[Exactness of the birth registry of Barcelona regarding birth weight and weeks of gestation].

OBJECTIVE: The aim of the study is to know the accuracy of the variables birth weight and gestational age in the Barcelona Birth Registry. Hospital medical records are used as gold standard. METHODS: A representative sample (n = 1,932) was selected from all the residents born in the city of Barcelona between 1st of May and 31st of December of 1996. The variables birth weight and gestational age were evaluated. Exhaustivity, sensitivity, specificity and predictive value for these variables were calculated. RESULTS: The Registry shows a high exhaustivity for the study variables. The lowest value of sensitivity corresponds to premature births (65.1%) and the lowest value of specificity to term births (63.9%). The predictive value positive was 77.5% for preterm births and 76.7% for term births. CONCLUSIONS: In general, exhaustivity and accuracy of the Barcelona Birth Registry are high, but sensitivity for preterm births in the Registry is lower. However, the corresponding maternal and child health indicators do not vary in an important manner.

Birth Certificates↗

PubMed2004

The prevalence and relationship between periodontal disease and pre-term low birth weight infants at King Khalid University Hospital in Riyadh, Saudi Arabia.

The aim of this study was to examine the prevalence and relationship between periodontal disease and pre-term low birth weight (PLBW) among Saudi mothers at King Khalid University Hospital (KKUH) in Riyadh, Saudi Arabia. The periodontal status and the relative risk were also analyzed. The study consisted of 30 cases [infants <37 weeks and/or weighing <2.500 kilograms (kg)] and a daily random sample of 60 controls [> 37 weeks and/or weighing >2.500 kg]. Clinical periodontal indices were measured on the labor wards. Associated risk factors for periodontal disease and PLBW were ascertained by means of a structured questionnaire and maternal notes. The prevalence of the PLBW was found to be 11.3%, and the prevalence of periodontal disease was high among the study population. The risk of PLBW remained high with increasing periodontal disease (odds ratio [OR] 4.21, 95% confident interval [CI] 1.99-8.93) despite controlling the other risk factors such as age, smoking, and social class. In conclusion, there is a correlation between periodontal disease and PLBW in KKUH.

Adolescent↗

PubMed2004

Beta2-adrenergic receptor gene polymorphisms and pregnancy outcome.

AIMS: The association between alleles at two loci of the polymorphic beta2-adrenergic receptor (beta2AR) gene and pregnancy outcome was determined. METHODS: In a case-control study, buccal swabs obtained from 159 mother-infant pairs after a preterm or term birth were analyzed by gene amplification and endonuclease digestion for polymorphisms at codons 16 and 27 of the beta2AR gene. RESULTS: Homozygosity for allele A at codon 16 (Arg-16) occurred in 26 (20.5%) of 127 mothers with a term birth and in none of the mothers who had a spontaneous preterm birth (p=0.002). Conversely, 24 of 32 (75.0%) mothers with a spontaneous preterm birth, as compared to 58 of 127 (45.7%) mothers with term births, were Arg-16/ allele G (Gly-16) heterozygotes (p=0.003). There was no relation between pregnancy outcome and infant genotype at codon 16 or maternal or infant genotypes at codon 27. The alleles at codon 16 and 27 were in linkage disequilibrium and the combinations of Arg-16-Gln-27 homozygosity (p=0.04) and Arg-16/Gly-16-Gln homozygous (p=0.01) were associated with a decreased and increased rate of spontaneous preterm birth, respectively. CONCLUSION: At codon 16 of the beta2-AR gene, maternal Arg-16 homozygosity protects against, and Gly-16 predisposes to spontaneous preterm birth.

Adult↗

PubMed2006

The association between low level exposures to ambient air pollution and term low birth weight: a retrospective cohort study.

BACKGROUND: Studies in areas with relatively high levels of air pollution have found some positive associations between exposures to ambient levels of air pollution and several birth outcomes including low birth weight (LBW). The purpose of this study was to examine the association between LBW among term infants and ambient air pollution, by trimester of exposure, in a region of lower level exposures. METHODS: The relationship between LBW and ambient levels of particulate matter up to 10 um in diameter (PM10), sulfur dioxide (SO2) and ground-level ozone (O3) was evaluated using the Nova Scotia Atlee Perinatal Database and ambient air monitoring data from the Environment Canada National Air Pollution Surveillance Network and the Nova Scotia Department of Environment. The cohort consisted of live singleton births (> or =37 weeks of gestation) between January 1, 1988 and December 31, 2000. Maternal exposures to air pollution were assigned to women living within 25 km of a monitoring station at the time of birth. Air pollution was evaluated as a continuous and categorical variable (using quartile exposures) for each trimester and relative risks were estimated from logistic regression, adjusted for confounding variables. RESULTS: There were 74,284 women with a term, singleton birth during the study period and with exposure data. In the analyses unadjusted for year of birth, first trimester exposures in the highest quartile for SO2 and PM10 suggested an increased risk of delivering a LBW infant (relative risk = 1.36, 95% confidence interval = 1.04 to 1.78 for SO2 exposure and relative risk = 1.33, 95% confidence interval = 1.02 to 1.74 for PM10). After adjustment for birth year, the relative risks were attenuated somewhat and not statistically significant. A dose-response relationship for SO2 was noted with increasing levels of exposure. No statistically significant effects were noted for ozone. CONCLUSION: Our results suggest that exposure during the first trimester to relatively low levels of some air pollutants may be associated with a reduction in birth weight in term-born infants. These findings have implications for the development of effective risk management strategies to minimize the public health impacts for pregnant women.

Adult↗

PubMed1997

Postnatal growth patterns of full-term low birth weight infants in Northeast Brazil are related to socioeconomic status.

Low birth weight has many adverse consequences, some of which might be ameliorated if there is good postnatal compensatory, or catch-up, growth. We monitored growth, morbidity and feeding patterns in a cohort of 133 full-term, low birth weight infants from poor families in Pernambuco, Brazil, and investigated the relative contributions of a number of socioeconomic, maternal and infant variables to postnatal growth. Growth was measured at 4, 8, 17, 26 and 52 wk of age. Differential growth patterns were most marked during the first 8 wk of life, and the gains in z-score during this interval were strongly associated with attained z-scores at 12 months (r = 0.62 for weight and 0.64 for length). In a multivariate model, socioeconomic variables explained 21.4% of the variation in maximum gain in weight-for-age z-score achieved during the 12-month period, maternal weight explained a further 4.4%, infant birth length 4.7% and neonatal illness 5.4%. For maximum gain in length-for-age z-score, socioeconomic variables accounted for 24.4% of the variance, maternal height 4.9%, maternal smoking 3.3% and neonatal illness 3.1%. We surmise that the early differential growth patterns are set in utero and are indirectly affected prenatally by socioeconomic status.

Anthropometry↗

PubMed2003

Adverse pregnancy outcome in users of sulfamethizole during pregnancy: a population-based observational study.

OBJECTIVE: To estimate the risk of adverse birth and neonatal outcome, and miscarriage in women who used sulfamethizole during pregnancy. METHODS: The association between use of sulfamethizole and adverse birth and neonatal outcome was investigated in a case-control and a cohort study in Denmark. We used data from the Prescription Database, the Birth Registry and the Hospital Discharge Registry in North Jutland County to study any association between sulfamethizole use and first recorded miscarriage. The cohort analysis included 3484 women who received a prescription for sulfamethizole from 30 days before conception to date of delivery, and 60175 women who did not use a sulphonamide-containing drug during pregnancy or 30 days before conception. The case-control analysis included 3347 women who had a miscarriage, of whom 90 had taken sulfamethizole, and 22599 primiparous controls who had a live birth. RESULTS: Among women who received prescriptions for sulfamethizole, adjusted odds ratios and 95% confidence intervals for adverse birth outcome were: malformation 1.17 (0.95-1.43); low birth weight 0.69 (0.49-0.98); pre-term birth 1.12 (0.97-1.30); stillbirth 1.02 (0.61-1.68); neonatal jaundice 1.14 (0.38-3.46); and for receiving a prescription for sulfamethizole within 1 week before miscarriage 1.66 (0.92-2.99). CONCLUSIONS: We found no increased risk of congenital malformation, stillbirth or pre-term birth, and no association between use of sulfamethizole late in pregnancy and risk of neonatal jaundice. There was an increased risk of miscarriage after exposure to sulfamethizole during the week before miscarriage, but further studies are needed to evaluate whether this increased risk is causal.

Abnormalities, Drug-Induced↗

PubMed2003

Azathioprine, mercaptopurine and birth outcome: a population-based cohort study.

BACKGROUND: Data on the safety of azathioprine and mercaptopurine during pregnancy are very sparse. AIM: To examine the risk of adverse birth outcomes in women who took up prescriptions for azathioprine or mercaptopurine during pregnancy. METHODS: This is a Danish cohort study based on data from a population-based prescription registry, the Danish Birth Registry and the Hospital Discharge Registry. To examine the risk of congenital malformations, we included nine pregnancies exposed 30 days before conception or during the first trimester. To examine perinatal mortality, pre-term birth and low birth weight, we included 10 pregnancies exposed during the entire pregnancy. Eleven different exposed women were included in the study. Outcomes were compared with those of 19 418 pregnancies in which no drugs were prescribed to the mothers. RESULTS: Fifty-five per cent of the exposed women had inflammatory bowel disease and 45% other diseases. Adjusted odds ratios for congenital malformations, perinatal mortality, pre-term birth and low birth weight were 6.7 (95% confidence interval, 1.4-32.4), 20.0 (2.5-161.4), 6.6 (1.7-25.9) and 3.8 (0.4-33.3), respectively. CONCLUSIONS: Our results suggest that there is an increased risk of congenital malformations, perinatal mortality and pre-term birth in children born to women treated with azathioprine or mercaptopurine during pregnancy. More data are needed to determine whether the associations are causal or occur through confounding.

Abnormalities, Drug-Induced↗

PubMed2005

Outcome of term breech births: 10-year experience at a district general hospital.

OBJECTIVE: To review the short and long term outcomes among singleton infants with breech presentation at term delivered in a geographically defined population over a 10-year period. DESIGN: Retrospective, cohort study. SETTING: District General Hospital. POPULATION: 1433 term breech infants alive at the onset of labour and born between January 1991 and December 2000. METHODS: Data abstracted from birth registers, neonatal discharge summaries and the child health database system were used to compare the short and long term outcomes of singleton term breech infants born by two different modes of delivery (prelabour caesarean section and vaginal or caesarean section in labour). Fisher's exact test was used to compare the categorical variables. MAIN OUTCOME MEASURES: Short term outcomes: perinatal mortality, Apgar scores, admission to the neonatal unit, birth trauma and neonatal convulsions. Long term outcomes: deaths during infancy, cerebral palsy, long term morbidity (development of special needs and special educational needs). RESULTS: Of 1433 singleton term infants in breech presentation at onset of labour, 881 (61.5%) were delivered vaginally or by caesarean section in labour and 552 (38.5%) were born by prelabour caesarean section. There were three (0.3%) non-malformed perinatal deaths among infants born by vaginal delivery or caesarean section in labour compared with none in the prelabour caesarean section cohort. Compared with infants born by prelabour caesarean section, those delivered vaginally or by caesarean section in labour were significantly more likely to have low 5-minute Apgar scores (0.9% vs 5.9%, P < 0.0001) and require admission to the neonatal unit (1.6% vs 4%, P= 0.0119). However, there was no significant difference in the long term morbidity between the two groups (5.3% in the vaginal/caesarean section in labour group vs 3.8% in the prelabour caesarean group, P= 0.26); no difference in rates of cerebral palsy; and none of the eight infant deaths were related to the mode of delivery. CONCLUSIONS: Vaginal breech delivery or caesarean section in labour was associated with a small but unequivocal increase in the short term mortality and morbidity. However, the long term outcome was not influenced by the mode of delivery.

Breech Presentation↗

PubMed1986

Bovine leptospirosis: experimental serovar hardjo infection.

Almost the full range of clinical signs observed in pregnant cattle naturally infected with Leptospira interrogans serovar hardjo was observed in this experimental study in which 22 heifers were infected by intraplacentome inoculation with serovar hardjo strains. These features included abortion, mummification, stillbirth, premature and term birth of weak calves and full-term birth of live apparently healthy calves. Leptospires were demonstrated in all but three calves by culture and or immunofluorescence.

Animals↗

PubMed1988

Changes in the pulmonary alveolar subphase at birth in term and premature lambs.

To study the changes in alveolar fluid at birth, we measured alveolar Cl- as soon as possible after onset of ventilation in 11 anesthetized lambs. The lambs ranged from 129 to 144 days gestation and were delivered by cesarean section. Subpleural alveoli were punctured with Cl- selective microelectrodes as soon as 5 min and as late as 135 min after the onset of mechanical ventilation. The [Cl-] was 151 +/- 7 mEq/liter (mean +/- SD, n = 11) in fetal lung fluid collected before ventilation. After about 40 min of ventilation, alveolar Cl- was not different from that in term lambs 24 to 72 h old (94 +/- 6 mEq/liter, n = 21). Assuming first order kinetics the mean t 1/2 was 10.4 min. There was no difference as a function of gestation. Thus, alveolar chloride decreases rapidly and alveolar fluid assumes a mature character very soon after the start of breathing in term and premature lambs. The onset of ventilation appeared to stimulate these rapid changes.

Animals↗

PubMed1994

Sequential changes in pulmonary epithelial permeability after birth in term and preterm rabbits.

We assessed sequential changes in the permeability properties of the pulmonary epithelium in spontaneously breathing, newborn term (30 days of gestation) and preterm (28 days) rabbit pups, using the rate of pulmonary clearance of 99mTc-DTPA (MW = 492) as an index of permeability. In term rabbits, clearance was faster at 1 h of age than at hourly timepoints thereafter (p < 0.05). In preterm rabbits, clearance rates measured from 1 to 5 h after birth were not quite significantly different (p = 0.0519) although the trend to slower clearance with increasing time after birth was significant. When term and preterm rabbits were compared, clearance was similar at 1 h after birth but was faster at both 2 and 3 h in the preterm rabbits (p < 0.05). Pulmonary epithelial permeability appears to be increased in the immediate postnatal period and the duration of increased permeability is longer in preterm rabbits. Because lung water content at birth is greater in the preterm rabbits, we speculate that the permeability changes may be associated with clearance of fetal lung liquid.

Animals↗

PubMed2005

Depression at birth in term infants exposed to maternal chorioamnionitis: does neonatal fever play a role?

OBJECTIVES: (1) To determine the incidence and the time course of elevated temperature following delivery in term infants with clinical chorioamnionitis (CHORIO) and (2) to determine if the extent of temperature elevation at birth is associated with increased likelihood of NICU Admissions, birth depression, or with short-term neurological abnormalities. DESIGN/METHODS: The infants were divided into two groups based on the median admission rectal temperature of 37.8 degrees C for the cohort. Depression at birth was defined as either the need of positive pressure ventilation for >2 minutes, intubation, or Apgar score <6 at 5 minutes. Neurological examination and assessment of encephalopathy (Sarnat staging) was performed at birth and daily thereafter, by one investigator blinded to temperature findings. RESULTS: Infants with higher rectal temperature at 30 minutes of life were more likely to be admitted to NICU: OR (2.8, 95% confidence interval (CI) [1.8 to 4.3]), and were more likely to have birth depression OR (3, 95% CI [1.4 to 6.5]). For infants in NICU, a rectal temperature above 37.8 degrees C was present in 87% in the delivery room, persisted in 47% at 30 minutes, and declined to a normal temperature at 60 minutes of life in the absence of medical interventions. There was no relationship between neurological scores and neonatal temperature. CONCLUSIONS: Term infants exposed to CHORIO who had a higher neonatal temperature at 30 minutes of life, were more likely to be admitted to the NICU and to have birth depression, than infants with lesser degree of temperature elevation after birth. Within the NICU group, the extent of temperature elevation was not associated with worse neurological outcomes.

Apgar Score↗

PubMed1998

Maternal body composition near term and birth weight.

OBJECTIVE: To assess the relative influence of maternal body composition at late gestation on birth weight. METHODS: Maternal body composition was estimated in 224 women near term using a deuterium dilution technique. Using a stepwise multiple linear regression analysis, we studied the association with birth weight of eight factors, including maternal fat-free mass and fat mass. RESULTS: Maternal fat-free-mass was the most important variable influencing birth weight (R2 = .144, P < .001), followed by maternal fat mass (R2 = .051, P < .001). Gestational age at delivery was the third strongest influence on birth weight (R2 = .047, P < .001). CONCLUSION: In late pregnancy, fat-free mass was the most important maternal body component associated with birth weight. The implementation of longitudinal studies could shed more light on the influence of maternal body composition on birth weight.

Adult↗

PubMed2026

Assessing the impact of maternal blood pressure during pregnancy on perinatal health: a wide-angled Mendelian randomization study.

BACKGROUND: Observational studies link high blood pressure in pregnancy to numerous adverse pregnancy and perinatal outcomes; however, findings may be affected by residual confounding or reverse causation. This study aimed to assess the causal effect of blood pressure during pregnancy on a range of pregnancy and perinatal outcomes. METHODS: We performed two-sample Mendelian randomization (MR) to assess the effect of systolic and diastolic blood pressure (SBP/DBP) during pregnancy on 16 primary and eight secondary adverse pregnancy and perinatal outcomes. We obtained genetic association data from large-scale meta-analyses of genome-wide association studies involving predominantly European ancestry individuals for SBP/DBP (N = 1,028,980), and pregnancy and perinatal outcomes (N = 74,368-714,899). We used inverse-variance weighted (IVW) MR for main analyses and MR-Egger, weighted median, weighted mode, multivariable MR, and IVW adjusted for fetal genetic effects for sensitivity analyses. RESULTS: A 10 mmHg higher genetically predicted maternal SBP increased the odds of gestational diabetes, induction of labour, low birth weight (LBW), small-for-gestational age (SGA), preterm birth (PTB), and neonatal intensive care unit (NICU) admission (OR ranging from 1.11 [95% CI 1.02 to 1.20] for NICU admission to 1.33 [1.26 to 1.41] for LBW); while decreasing the odds of high birth weight (HBW), large-for-gestational age (LGA), and post-term birth [OR ranging from 0.76 (0.69 to 0.83) for HBW to 0.94 (0.90 to 0.99) for post-term birth]. We did not find evidence that genetically predicted higher maternal SBP was related to miscarriage or stillbirth. The results for maternal DBP were similar to the results for SBP. Overall, the main results were consistent across sensitivity analyses accounting for pleiotropic instruments and fetal genetic effects. CONCLUSIONS: Higher maternal blood pressure reduces gestation duration and fetal growth and increases the risks of induction of labour, gestational diabetes, and neonatal intensive care unit admission. This and other emerging evidence highlight the value of interventions aimed at controlling blood pressure in the population to reduce the burden of adverse pregnancy outcomes.

Humans↗

PubMed2005

Prenatal and perinatal correlates of adult mammographic breast density.

BACKGROUND: Adult mammographic percent density is one of the strongest known risk factors for breast cancer. In utero exposure to high levels of endogenous estrogens (or other pregnancy hormones) has been hypothesized to increase breast cancer risk in later life. We examined the hypothesis that those factors associated with higher levels of estrogen during pregnancy or shortly after birth are associated with higher mammographic breast density in adulthood. METHODS: We analyzed data on 1,893 women from 360 families in the Minnesota Breast Cancer Family Study who had screening mammograms, risk factor data, over age 40, and no history of breast cancer. Prenatal and perinatal risk factor data were ascertained using a mailed questionnaire. Mammographic percent density and dense area were estimated from the mediolateral oblique view using Cumulus, a computer-assisted thresholding program. Linear mixed effects models incorporating familial correlation were used to assess the association of risk factors with percent density, adjusting for age, weight, and other breast cancer risk factors, all at time of mammography. RESULTS: The mean age at mammography was 60.4 years (range, 40-91 years), and 76% were postmenopausal. Among postmenopausal women, there was a positive association of birthweight with percent density (P trend <0.01), with an adjusted mean percent density of 17.1% for <2.95 kg versus 21.0% for > or = 3.75 kg. There were suggestive positive associations with gestational age (mean percent density of 16.7% for preterm birth, 20.2% for term birth, and 23.0% for late birth; P trend = 0.07), maternal eclampsia/preeclampsia (mean percent density of 19.9% for no and 14.6% for yes; P = 0.16), and being breast-fed as an infant (mean percent density of 18.2% for never and 20.0% for ever; P = 0.08). There was no association of percent density with maternal age, birth order, maternal use of alcohol or cigarettes, or neonatal jaundice. Except for being breast-fed, these associations showed similar but attenuated trends among premenopausal women, although none were statistically significant. The results for dense area paralleled the percent density results. The associations of gestational age and being breast-fed as an infant with percent density attenuated when included in the same model as birthweight. CONCLUSIONS: Birthweight was positively associated with mammographic breast density and dense area among postmenopausal women and more weakly among premenopausal women, suggesting that it may be a marker of this early life exposure. These results offer some support to the hypothesis that pregnancy estrogens or other pregnancy changes may play a role in breast cancer etiology, and suggest that these factors may act in part through long-term effects on breast density.

Adult↗

PubMed2006

The effects of smoking and hypertensive disorders on fetal growth.

BACKGROUND: It is well known that smoking and pregnancy induced hypertension (PIH) are associated with decreased fetal growth. It has been reported that in preeclampsia the fetal growth deficit attributable to smoking is higher, which has been contradicted in other studies. We therefore evaluated the effects on fetal growth of early- and late onset PIH and chronic hypertension and how cigarette smoking modify these effects. We also quantified the proportion of small for gestational age (SGA) cases attributable to PIH, chronic hypertension, and smoking. METHODS: Population-based study based on record of 215598 singleton pregnancies from the Medical Birth Registry of Norway. RESULTS: In severe preeclampsia, mild preeclampsia, transient hypertension, and normotension in term birth, odds ratios (ORs) of SGA in smokers compared with non-smokers were 1.4 (95% confidence interval 0.9, 2.2), 1.6 (1.3, 1.9), 2.3 (1.8, 3.1), and 2.0 (1.9, 2.1), respectively. For preterm births, corresponding ORs were 1.3 (0.9, 2.0), 1.8 (1.1, 3.0), 4.1 (1.9, 9.0), and 1.7 (1.4, 2.0), respectively. The effect of early onset PIH was stronger than that in term births, while the effect of smoking was equal in preterm and term newborns. Only in non-smokers who delivered at term, the rates of SGA significantly increased with the severity of PIH (ORs = 1.3 (1.1, 1.5), 1.8 (1.7, 2.0), and 2.5 (2.2, 3.0) for transient hypertension, mild-, and severe preeclampsia, respectively). The combined effects of smoking and hypertension were generally not synergistic. The effect of smoking was not stronger in women who had chronic hypertension. Nor were the effects of chronic hypertension stronger in smokers. PIH explained 21.9 and 2.5% of preterm and term cases of SGA, respectively, while smoking explained 12% of SGA cases. CONCLUSION: The effects of hypertensive disorder and smoking were generally not synergistic, which suggest that they may exert their main actions on separate sites or work through separate mechanisms within or outside the placenta. If smoking were eliminated in pregnant women, the number of SGA cases would be reduced by 12%.

Journal Article↗

PubMed1994

[Maturation of generalized motility, spontaneous during sleep, from birth at term to the age of 6 months].

This work analysed the evolution of generalized motility from normal birth (39 to 40 weeks of gestational age) to six months of age, in 73 healthy infants during sleep, according to age. Sleep polygraphic recordings were performed in the morning; body movements were recorded with piezo-electric accelerometers. Our results showed that the number of movements per sleep hour was higher in active sleep (AS) as compared to quiet sleep (QS) whatever the age although the difference was less important in neonates (P < 0.05) than after one month of life (P < 0.001). The number of movements and the percentage of time spent in movements decreased with age; however in QS these parameters decreased sharply from birth to one month and a half but then did not significantly differ; in AS they became progressively lower. There were no statistically significant differences in the duration of body movements between sleep states in each age group; their mean duration became shorter from birth to six months of age (in AS P < 0.0001 and in QS P < 0.05). The distributions of the number of movements throughout the sleep stage were different according to sleep state and age. The movements were equally distributed during AS whatever the age and in the neonate group during QS; in older infants, the number of movements increased at the beginning and at the end of QS stages. During the first six months of life, spontaneous motility during sleep was inhibited, however, this process differed in quiet and active sleep. The relationship between body movements and sleep stages' organisation became closer during maturation.

Child Development↗

PubMed2002

Fetal sex and preterm birth: are males at greater risk?

BACKGROUND: The existence of a male excess among preterm births is interesting because it could shed light on the aetiology of preterm birth. Possible mechanisms are greater body weight, increased susceptibility to complications of pregnancy, sex-linked biochemical processes and earlier conception in the fertile cycle. METHODS: We measured the association between fetal sex and preterm birth in four original datasets, including a cohort of births after IVF, and 20 populations extracted from published birthweight references. The original samples were also analysed by mode of onset. RESULTS: There were more males among preterm and early preterm births than among term births in most populations, including IVF births (odds ratio: 1.09-1.24). No male excess was observed for two cohorts of black births, induced preterm births in the general population, and spontaneous onset births after IVF. CONCLUSIONS: The proportion of male births declines with increasing gestation, even when time of conception is known. This male excess appears to be strongest for spontaneous preterm births. Studying the sex ratio of preterm births by medical risk factors may clarify why the male excess is absent in some populations. The possibility that obstetric decision-making affects the sex ratio of indicated births must be considered.

Birth Weight↗