Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “First Birth”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21Linked to original sources
PubMed2006

The hysterectomized woman. Is she special? The women's health in the Lund area (WHILA) study.

OBJECTIVE: To delineate the health profile of hysterectomized women and to assess whether women who have undergone hysterectomy have a different health profile even before surgery. MATERIAL AND METHODS: The WHILA project covers all women (n = 10,766) aged 50-60, living in the Lund area and are based on questionnaires and personal interviews tied to laboratory examinations. RESULTS: 6917 women (64.2%) had complete questionnaires and laboratory tests, 800 were hysterectomized (11.6%). Logistic regression analysis revealed that hysterectomized women had more "dizziness" 1.40 (1.19-1.66), "nervous problems" 1.29 (1.07-1.56), "backache" 1.37 (1.16-1.62), "joint problems" 1.29 (1.09-1.52), "eye problem" 1.20 (1.02-1.42) and "headache" 1.17 (1.00-1.37). For both somatic (5.22 versus 4.49 mean value, p < 0.001) and psychological (4.19 versus 3.86 mean value, p = 0.002) symptoms, the number was higher in hysterectomized women. Logistic regression analysis revealed that among hysterectomized women university education was less common odds ratios 0.73 (95% confidence interval 0.58-0.91) as well as working full time 0.76 (0.62-0.93). A higher body weight at the age 25, 1.01 (1.001-1.02) as well as a weight gain of more than 5 kg during the last 5 years 1.27 (1.07-1.50), elevation of serum triglycerides 1.29 (1.16-1.44), high-density (HDL) 1.44 (1.14-1.80) and low-density lipoprotein (LDL) cholesterol 1.11 (1.02-1.21) as well as the bone density 1.08 (1.00-1.17). Hysterectomized women had a lower age at giving first birth (p < 0.001), shorter interval between menstrual periods (p < or = 0.001) and less frequent amenorrhic episodes (p < 0.05). The hysterectomized women used IUD to a lesser extent (p < 0.05) but used hormone therapy (HT) (p < 0.001) and utilized health care services (p < 0.001) more often. CONCLUSIONS: Long after surgery, several somatic and psychological symptoms were still more common in hysterectomized women. A low frequency of amenorrhic episodes and lower age at giving first birth, concomitant with a higher body weight already at age 25 may imply that women who end up hysterectomized have a specific health profile long before as well as long after surgery.

Age Factors↗
PubMedDate not supplied

Models of breast cancer show that risk is set by events of early life: prevention efforts must shift focus.

We have recently published a mathematical model of the etiology of breast cancer based on the data from the Nurses Health Study that extends the Pike model of breast cancer (see Appendix). The most salient feature of the model is that it identifies the years before the first birth of a child as the most crucial in establishing future risk of breast cancer. The extended model includes several additional details of reproductive risk factors, allowing us to quantify the relative importance of each of the reproductive risk factors and to estimate the effect of changes in key determinants of breast cancer. In this review, we present the evidence from both animal studies and epidemiological research that corroborate the critical importance of the exposures that occur before first birth. We argue that research and preventive interventions should now focus on youth. Population-wide prevention strategies are necessary because the inherited genetic risk for breast cancer accounts for no more than 10-15% of all breast cancer cases, leaving 85% of cases diagnosed among women who are not in this high-risk subgroup of the population. An example of a population-based intervention would be the promotion of increased physical activity among young girls that could result in the delay of menarche. An example of additional research that focuses on the importance of early life exposures would be an analysis of the relation between diet and other lifestyle factors during adolescence and the subsequent risk of breast cancer and studies of precursor lesions (atypical hyperplasia). Shifting the focus of breast cancer prevention to this age group is urgently needed.

Age Factors↗
PubMed2006

Reproductive factors, exogenous hormone use and bladder cancer risk in a prospective study.

Sex is a consistent predictor of bladder cancer: men experience 2-4-fold higher age-adjusted rates than women in the U.S. and Europe. The objective of this study was to examine whether hormone-related factors are associated with bladder cancer in women. We examined parity, age at menarche, age at first birth, age at menopause, oral contraceptive use and menopausal hormone therapy (HT) use and bladder cancer risk in the Breast Cancer Detection Demonstration Project Follow-Up Study. Endpoint and exposure information was collected on 54,308 women, using annual telephone interviews (1980-86) and 3 mailed, self-administered questionnaires (1987-98). During an average follow-up time of 15.3 years, 167 cases of bladder cancer were identified. Univariate and adjusted rate ratios (RRs) were estimated using Poisson regression. Parity, age at menarche, age at first birth, age at menopause, and oral contraceptive use were not associated with bladder cancer risk. The majority of menopausal women who took HT used estrogen therapy (ET). Postmenopausal women with less than 4 years, 4-9 years, 10-19 years and 20 or more years of ET use had RRs of 1.55 (95% CI = 0.96-2.51), 1.00 (95% CI = 0.49-2.04), 1.23 (95% CI = 0.62-2.43) and 0.57 (95% CI = 0.14-2.34), respectively, compared with nonusers (p = 0.50). Findings from this study are not consistent with the hypothesis that hormone-related factors in women are associated with bladder cancer.

Age Factors↗
PubMed1992

Risk factors for breast cancer by age and menopausal status: a case-control study in Singapore.

A case-control study was conducted among Singapore Chinese women, comprised of 200 histologically confirmed cases of breast cancer and 420 hospital controls. Subjects were interviewed on family history of breast cancer, social and demographic characteristics, reproductive history, and diet one year prior to interview. Differences in risk factors were observed according to menopausal status. In the premenopausal group, the most consistently significant nondietary effect was an increased risk with late age at first birth. In postmenopausal women, the most consistent nondietary effects were increased risks with nulliparity, tall stature, high educational status, and a family history of breast cancer. In premenopausal women, the strongest dietary effects were low risks with high intakes of polyunsaturated fatty acids (PUFA), beta-carotene, soya protein as a proportion of all protein, and a high risk with high red-meat intake. No dietary effects were observed in postmenopausal women. Examination of effects by 10-year age groups suggested that the differences in the effects of age at first birth, nulliparity, height, education, beta-carotene intake, and PUFA intake between premenopausal and postmenopausal women were at least partly attributable to age-related differences in the baseline distributions of these variables. The variation in the effects of red meat and soya protein appeared to be attributable mainly to menopausal status itself, which is consistent with the hypothesis that these factors operate on risk by way of hormonal mechanisms.

Adult↗
PubMed1975

[A decrease in twin births and factors involved in multiple pregnancy].

The object of this investigation were the causes of the decrease of the frequency of twin births during the last two decades. In Moscow this frequency decreased from 1,19% in 1956 to 0,7% in 1973. Among the births the proportion of first births was observed to increase, as well as the proportion of very young mothers. The effect of this process on the women characterized by a tendency to polyembryony was more conspicuous, than in the average on the population as a whole. During the last decades the process of acceleration of puberty was observed both in the mothers of twins and in all the women in general. However a somewhat later onset of first menstruations is characteristic of the women having a tendency to polyembryony-Hormonal changes taking place in the course of acceleration are apparently one of the causes of the decrease of the twin births frequency.

Adolescent↗
PubMed2005

Reproductive factors and subtypes of breast cancer defined by hormone receptor and histology.

Reproductive factors are associated with reduced risk of breast cancer, but less is known about whether there is differential protection against subtypes of breast cancer. Assuming reproductive factors act through hormonal mechanisms they should protect predominantly against cancers expressing oestrogen (ER) and progesterone (PR) receptors. We examined the effect of reproductive factors on subgroups of tumours defined by hormone receptor status as well as histology using data from the NIHCD Women's Contraceptive and Reproductive Experiences (CARE) Study, a multicenter case-control study of breast cancer. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) as measures of relative risk using multivariate unconditional logistic regression methods. Multiparity and early age at first birth were associated with reduced relative risk of ER + PR + tumours (P for trend=0.0001 and 0.01, respectively), but not of ER - PR - tumours (P for trend=0.27 and 0.85), whereas duration of breastfeeding was associated with lower relative risk of both receptor-positive (P for trend=0.0002) and receptor-negative tumours (P=0.0004). Our results were consistent across subgroups of women based on age and ethnicity. We found few significant differences by histologic subtype, although the strongest protective effect of multiparity was seen for mixed ductolobular tumours. Our results indicate that parity and age at first birth are associated with reduced risk of receptor-positive tumours only, while lactation is associated with reduced risk of both receptor-positive and -negative tumours. This suggests that parity and lactation act through different mechanisms. This study also suggests that reproductive factors have similar protective effects on breast tumours of lobular and ductal origin.

Adult↗
PubMed2004

A population-based study on the risk of cervical cancer and cervical intraepithelial neoplasia among grand multiparous women in Finland.

Previous studies suggest that high parity increases the risk of cervical cancer. We studied the risk of cervical cancer (CC) and cervical intraepithelial neoplasia (CIN3) in a Finnish cohort of grand multiparous (GM) women (at least five children) with low prevalence of sexually transmitted infections (STI). The Finnish Cancer Registry data revealed 220 CC and 178 CIN3 cases among 86 978 GM women. Standardised incidence ratios (SIR) were calculated from the numbers of observed and expected cases. Interval analyses by parity, age at first birth and average birth interval were done using multivariate Poisson regression. Seroprevalence of human papillomavirus (HPV) 16 and Chlamydia trachomatis was tested among 561 GM women and 5703 women with 2-4 pregnancies. The incidence among GM women was slightly above the national average for squamous cell carcinoma of cervix uteri (SIR 1.21, 95% CI 1.05-1.40) and CIN3 (1.37, 95% CI 1.17-1.58), but lower for adenocarcinoma (SIR 0.77, 95% CI 0.52-1.10). The seroprevalence of HPV16 and Chlamydia trachomatis among GM women was lower than in the reference population, except among those women who had their child under age 19. Age under 20 years at first birth increased the risk of CC and CIN3 especially in premenopausal GM women, while increasing parity had no effect. The small relative risks of CC and CIN3 among GM women in our study as compared to studies from other countries can be explained by the exceptionally low prevalence of STIs in Finnish GM women. The observed SIRs between 1.2 and 1.4 should be interpreted to represent increased risk attributable to grand multiparity. The increased incidence of CC and CIN3 among young GM women suggests causal association to HPV 16 and Chlamydia trachomatis infections.

Adenocarcinoma↗
PubMed2001

Childhood poverty, early motherhood and adult social exclusion.

Childhood poverty and early parenthood are both high on the current political agenda. The key new issue that this research addresses is the relative importance of childhood poverty and of early motherhood as correlates of outcomes later in life. How far are the 'effects' of early motherhood on later outcomes due to childhood precursors, especially experience of childhood poverty? Subsidiary questions relate to the magnitude of these associations, the particular levels of childhood poverty that prove most critical, and whether, as often assumed, only teenage mothers are subsequently disadvantaged, or are those who have their first birth in their early twenties similarly disadvantaged? The source of data for this study is the National Child Development Study. We examine outcomes at age 33 for several domains of adult social exclusion: welfare, socio-economic, physical health, emotional well-being and demographic behaviour. We control for a wide range of childhood factors: poverty; social class of origin and of father; mother's and father's school leaving age; family structure; housing tenure; mother's and father's interest in education; personality attributes; performance on educational tests; and contact with the police by age 16. There are clear associations for the adult outcomes with age at first birth, even after controlling for childhood poverty and the other childhood background factors. Moreover, we demonstrate that the widest gulf in adult outcomes occurs for those who enter motherhood early (before age 23), though further reinforced by teenage motherhood for most adult outcomes. We also show that any experience of childhood poverty is clearly associated with adverse outcomes in adulthood, with reinforcement for higher levels of childhood poverty for a few outcomes.

Adolescent↗
PubMed1981

Breast cancer incidence in women with a history of progesterone deficiency.

In order to investigate the nature of the association of involuntarily delayed first birth and risk of breast cancer, 1083 white women who had been evaluated and treated for infertility from 1945-1965 were followed prospectively through April 1978 to ascertain their breast cancer incidence. These women were categorized as to the cause of infertility into two groups, those with endogenous progesterone deficiency (PD) and those with nonhormonal causes (NH). Women in the PD group had 5.4 times the risk of premenopausal breast cancer compared to women in the NH group. This excess risk could not be explained by differences between the two groups in ages at menarche or menopause, history of oral contraceptive use, history of benign breast disease or age at first birth. Women in the PD group also experienced a 10-fold increase in deaths from all malignant neoplasms compared to the NH group. The incidence of postmenopausal breast cancer did not differ significantly between the two groups.

Adult↗
PubMed2005

Labour-market status and first-time parenthood: the experience of immigrant women in Sweden, 1981-97.

This paper investigates the impact of labour-market attachment on first births of foreign-born women in Sweden. The study uses a longitudinal, register-based dataset consisting of the entire population of immigrants from ten nations and a 5-per-cent random sample of natives. The effects of earned income are evident, with increased income levels increasing the probability of becoming a mother for all observed nationalities. The effects of various forms of participation and non-participation in the labour force do not vary greatly between immigrants and the Swedish-born. Among all subgroups, we find a higher propensity to begin childbearing among those who are established in the labour market. Contrary to popular belief, receiving welfare benefits clearly reduces first-birth intensity for immigrants but not for natives. The similarity in patterns across widely different national groups supports the notion that various institutional factors affecting all subgroups are crucial in influencing childbearing behaviour.

Adolescent↗
PubMed1995

Reproductive factors and family history of breast cancer in relation to plasma estrogen and prolactin levels in postmenopausal women in the Nurses' Health Study (United States).

Parity, age at first birth, age at menarche, and a family history of breast cancer have each been associated consistently with breast cancer risk. Whether this increase in risk is mediated, at least in part, through changes in endogenous hormone levels is unclear. We conducted a cross-sectional study of the relationships between these factors and plasma hormone levels in 216 healthy postmenopausal women in the Nurses' Health Study (United States). The hormones evaluated were estradiol, percent and total free estradiol, percent and total bioavailable estradiol, estrone, estrone sulfate, and prolactin. After controlling for age, body mass index (weight/height2), and alcohol use, we observed inverse associations between estrone sulfate and parity (r = -0.15, P = 0.03) and between percent bioavailable estradiol and age at first birth (r = -0.17, P = 0.02). Although women with a family history of breast cancer tended to have higher estrogen levels compared with women without such history, the differences were not statistically significant. Age at menarche was not related significantly to any of the hormones. These data provide some additional evidence that the inverse relationship observed between parity and breast cancer risk may be mediated, at least in part, through decreased estrogen levels. Our data do not support a substantial influence of either family history of breast cancer or age at menarche on postmenopausal estrogen or prolactin levels.

Adult↗
PubMed2002

Breast cancer risk in Ashkenazi BRCA1/2 mutation carriers: effects of reproductive history.

BACKGROUND: Younger age at first birth and greater parity generally reduce the risk of developing breast cancer, but whether this reduced risk holds in women with a mutation in the BRCA1 or BRCA2 gene is unknown. METHODS: In a Washington DC community-based study conducted in 1996, we tested 5318 Ashkenazi Jews for three BRCA1/2 founder mutations and identified 120 mutation carriers. Applying an extension of the "kin-cohort" analysis, we compared the effects of reproduction on breast cancer risk in carriers and noncarriers. We also used a case-case analysis among 288 participants who had been diagnosed with breast cancer. RESULTS: In noncarriers, the estimated relative risk (RR) of breast cancer rose 5% with each 5-year increment in age at first birth (RR = 1.05; 95% confidence interval [CI] = 0.97-1.15). By contrast, the estimated risk in mutation carriers fell with each 5-year increment in age (RR = 0.65; 95% CI = 0.37-1.16). Among the 288 participants who were breast cancer survivors themselves, the comparison of carriers with noncarriers also showed no protection associated with early birth in the presence of a mutation in BRCA1 or BRCA2. CONCLUSIONS: It is not yet clear whether the recognized breast cancer risk factors operate in the same way in women who carry a mutation in the BRCA1 or BRCA2 genes.

Adult↗
PubMed1992

The role of age at menarche and at menopause on breast cancer risk: combined evidence from four case-control studies.

The role of age at menarche and at menopause on breast cancer risk was reassessed in a combined analysis of four Italian case-control studies including a total of 6,075 cases and 5,492 controls. The risk of breast cancer was lower in women whose menarche occurred at age 15 or over, but there was no evidence for the risk to increase with decreasing age at menarche below age 15. Compared with women with earlier menarche, the relative risk (RR) was 0.9 (95% confidence interval, CI 0.7-1.0) for those with menarche at age 15, 0.8 (95% CI 0.6-0.9) for menarche at 16, and 0.7 (95% CI 0.5-0.8) for menarche at age 17 or over. There was no significant interaction between age at menarche and study centre or age at diagnosis, parity and age at first birth. In relation to age at menopause, compared with women whose menopause occurred at age 40 or less, the relative risk was 1.1 (95% CI 0.8-1.3) between 40 and 44, 1.2 (95% CI 0.9-1.4) between 45 and 49, 1.4 (95% CI 1.2-1.8) between 50 and 53, and 1.4 (95% CI 1.1-1.8) above 53. The risk estimates were comparable in various studies, and the trend in risk with age at menopause was statistically significant. The risk estimates tended to be somewhat higher at peri-menopausal age (45 to 54 years), but no consistent pattern was evident across subsequent strata of age, and the interaction with age was not significant. Likewise, no consistent interaction was observed with parity, age at first birth or body mass index.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

The health consequences of teenage fertility.

A review of the literature on the health consequences of teenage pregnancy and childbirth shows remarkable similarity in findings from studies conducted in the United States, Canada, Britain, France and Sweden. In particular, results of studies conducted since 1970 have tended to indicate that the increased risk of maternal complications from pregnancy and delivery among teenagers--especially those older than 15--is associated more with socioeconomic factors than with the biological effects of age. Smaller differences in maternal mortality between teenagers and older women exist in England and Wales than in the United States and France; this finding suggests that England and Wales may have minimized the age or socioeconomic factors contributing to a difference in rates. Inadequate prenatal care may be a major cause of pregnancy-related complications for mothers, since teenagers in all countries are more likely than older mothers to seek care late in the pregnancy or not all. There is a very marked association between young age of mother and low birth weight in all countries. Sweden has the lowest rate of low birth weight at all maternal ages, and the United States generally has the highest. Some of the apparent effect of young maternal age on birth weight may be because the birth is likely to be the mother's first, and first births have a higher incidence of prematurity. As in the case of maternal health, inadequate prenatal care has been singled out as an important determinant of both prematurity and low birth weight. Late fetal death rates in the United States, England and Wales, and France are slightly higher among teenagers than among women in their 20s. In Canada and Sweden, however, no substantially increased risk for young women is found. Perinatal death rates, which one might expect to be influenced more by environmental factors than are late fetal deaths, show a more marked increase among infants of teenagers than do rates of late fetal deaths. Again, Sweden does not fit the pattern. Studies that separate data for young teens and older teenage mothers also indicate that increased perinatal and late fetal mortality rates may occur only among very young teenage mothers. There is no evidence of an overall increase in congenital malformations among babies born to teenagers. When individual birth defects are examined, some studies have shown increased rates of cardiovascular and central nervous system malformations among the children of teenage mothers.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1998

Coffee consumption and the risk of breast cancer.

On the basis of clinical observations that some women with fibrocystic breast disease experienced resolution of the disease on eliminating methylxanthines from their diet, it has been suggested that coffee intake might be related to breast carcinogenesis. The relationship between coffee (mostly expresso and mocha), decaffeinated coffee and tea intake and breast cancer risk was therefore considered, combining data from two case-control studies, conducted in Italy between 1983 and 1994. Cases were 5,984 women, below age 75, with histologically confirmed breast cancer, and controls were 5,504 women admitted to hospital for a wide spectrum of acute, non-neoplastic, non-hormone-related diseases. The odds ratios (ORs) were estimated from multiple logistic regression equations including terms for study/centre, age, education, body mass index, smoking status, total alcohol intake, age at menarche and menopause, parity and age at first birth, use of oral contraceptives, use of hormone replacement therapy, history of benign breast disease and family history of breast cancer. No relationship was observed between coffee intake and the risk of breast cancer. The multivariate ORs were 1.17 (1.03-1.33), 1.17 (1.04-1.33), 1.21 (1.06-1.37) and 0.96 (0.83-1.11) for women drinking < 2, 2, > 2 to < 4 and > or = 4 cups/day compared to non-drinkers. Decaffeinated coffee was consumed only by 6-7% of cases and controls and the corresponding OR was 0.84 (0.72-0.98). Tea consumption was also low and not associated with the risk of breast cancer (OR 0.94, 95% CI 0.85-1.03). No significant heterogeneity was found for coffee intake across strata of age at diagnosis, education, body mass index, smoking status, total alcohol intake, age at menarche and menopause, parity, age at first birth, ever use of oral contraceptives, hormone replacement therapy, history of benign breast disease and family history of breast cancer. Thus, this study, based on a large data set, allows us to exclude the hypothesis that coffee intake is related to breast cancer risk in this Italian population.

Adult↗
PubMed2006

Risk factors for hormone receptor-defined breast cancer in postmenopausal women.

The effect of classic breast cancer risk factors on hormone receptor-defined breast cancer is not fully clarified. We explored these associations in a Swedish population-based study. Postmenopausal women ages 50 to 74 years, diagnosed with invasive breast cancer during 1993 to 1995, were compared with 3,065 age frequency-matched controls. We identified 332 estrogen receptor (ER-) and progesterone receptor (PR-) negative, 286 ER+PR-, 71 ER-PR+, 1,165 ER+PR+, and 789 tumors with unknown receptor status. Unconditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI). Women ages >or=30 years, compared with those ages 20 to 24 years at first birth, were at an increased risk of ER+PR+ tumors (OR, 1.5; 95% CI, 1.2-1.8) but not ER-PR- tumors (OR, 1.1; 95% CI, 0.8-1.6). Women who gained >or=30 kg in weight during adulthood had an approximately 3-fold increased relative risk of ER+PR+ tumors (OR, 2.7; 95% CI, 1.9-3.8), but no risk increase of ER-PR- tumors (OR, 1.0; 95% CI, 0.5-2.1), compared with women who gained <10 kg. Compared with never users, women who used menopausal estrogen-progestin therapy for at least 5 years were at increased risk of ER+PR+ tumors (OR, 3.0; 95% CI, 2.1-4.1) but not ER-PR- tumors (OR, 1.3; 95% CI, 0.7-2.5). In conclusion, other risk factors were similarly related to breast cancer regardless of receptor status, but high age at first birth, substantial weight gain in adult age, and use of menopausal estrogen-progestin therapy were more strongly related to receptor-positive breast cancer than receptor-negative breast cancer.

Aged↗
PubMed1990

Infertility and breast cancer: a population-based case-control study.

To investigate whether a history of infertility affects a woman's risk of developing breast cancer, the authors analyzed case-control data collected between 1980 and 1982 as part of the Cancer and Steroid Hormone Study. The 4,730 cases were women aged 20-54 years with a first diagnosis of breast cancer ascertained from eight population-based cancer registries; the 4,688 controls were women randomly selected from the general population of these same eight areas. After controlling for age, age at first birth, and parity, the odds ratio (OR) for breast cancer associated with infertility was 1.01 (95% confidence interval (CI) 0.89-1.15) among gravid women. Controlling for age, the odds ratio was 0.82 (95% CI 0.59-1.14) among nulligravid women. Women who reported that the reason for their infertility was a problem with their ovaries had a risk similar to that for women without a history of infertility (OR = 0.75, 95% CI 0.48-1.24). Women whose physicians reported that the reason for their infertility was anovulation or Stein-Leventhal syndrome also had risks similar to those for women without a history of infertility (OR = 1.26 (95% CI 0.67-2.34) and OR = 1.13 (95% CI 0.46-2.78), respectively). Menopausal status, age at menarche, history of spontaneous abortions, drinking or smoking behavior, use of exogenous hormones, or family history of breast cancer did not appreciably alter the observed odds ratios. If infertility has an effect on breast cancer that is independent of age at first birth, then the effect is small.

Adult↗
PubMed1985

Estrogen and sex hormone-binding globulin levels in nulliparous and parous women.

The hormone profiles of nulliparous and parous women on day 11 of their menstrual cycle have been studied in an attempt to seek evidence for the hormonal basis of the protective effect of first birth on breast cancer risk. A previous publication reported that there were significantly lower (26%) early morning prolactin levels in parous women as compared to those levels in nulliparous women but that there were no differences in plasma and urinary estrogen levels. The present study shows, however, that parous women had significantly shorter cycle lengths than nulliparous women of the same age, and the data were reevaluated with this difference being taken into account. After adjustment for cycle length (within the range of 24-32 days) and age, estrogen levels were significantly lower (22%) in parous women compared to those in nulliparous women. Two further aspects of estrogen metabolism were measured in the plasma samples of these women: the binding capacity of sex hormone-binding globulin (SHBG) and the percentage of free estradiol (E2). SHBG levels were 12% higher in parous women, but there was no difference in percentage of free E2. In the previous publication it was suggested that the protective effect of first birth on breast cancer risk was mediated in part by permanently lowering prolactin levels. The current findings suggest that changes in estrogen metabolism also are a factor.

Adult↗