The majority of women in the current analysis were from the DESAD cohort (). Exposed women were somewhat younger than unexposed women, and correspondingly, were younger at first enrollment into the study, when age at menarche was ascertained. Highest level of education was similar among the exposed and unexposed daughters, although slightly more exposed had college degrees or higher. DES-exposed mothers were slightly older at the index pregnancy than unexposed mothers. There was little difference in maternal smoking during pregnancy in the DESAD cohort (). Information on maternal smoking was missing for 62% of the Dieckmann cohort.
Characteristics of women prenatally exposed and unexposed to diethylstilbestrol
DES exposure was associated with a small reduction in the mean length of gestation. Overall, the mean difference in gestational length, comparing DES-exposed with unexposed women, was −0.63 weeks (95% confidence interval (CI) = (−0.78, −0.49), after adjustment for cohort (). There was a greater reduction in the DESAD (−0.66 weeks) than the Dieckmann (−0.51 weeks) cohort. Further adjustment for maternal age, maternal smoking, and year of birth in the DESAD participants with complete information on those variables (94%) attenuated the estimate somewhat (−0.61 vs. −0.66 weeks). The average gestational length was shorter in the high dose cohort compared to those in the low dose cohort (mean difference between exposed and unexposed: −0.77 vs. −0.43 weeks, respectively, ). In analyses stratified by cumulative total dose in the subset of DESAD women with complete information on dose, higher dose appeared to be associated with shorter gestational length, although the trend was not monotonic by dose category. Earlier exposure to DES during gestation also was associated with shorter gestational length, compared to the unexposed (). Among exposed women only, exposure before eight weeks was also related to shorter length of gestation compared to those exposed at a gestational age of 15 weeks or later (mean difference=−0.49 weeks, 95%CI=−0.72, −0.27).
Difference in mean gestational length and odds ratios (95% CI) for preterm birth by DES exposure status, cohort, and dose and gestational age of first exposure to DES
Risk of having been born early (<37 weeks) was elevated in the DES exposed, compared to the unexposed (OR=2.97; 95% CI=2.27, 3.87) (). This association was stronger in the DESAD (OR=3.22; 95% CI=2.39, 4.33) than in the Dieckmann cohort (OR=1.98; 95% CI=1.05, 3.74). The estimates for very preterm birth (<34 weeks) were also elevated in both cohorts (OR=3.92 (95% CI=2.05, 7.50) and 3.07 (95% CI=1.00, 9.48), for DESAD and Dieckmann, respectively). The effect estimates were slightly higher in those originating from the high dose cohorts (OR=3.29) compared to the low dose cohorts (OR=2.54) (). Control for maternal age, smoking, and year of birth did not have an appreciable effect on the estimates (data not shown). In the DESAD cohort, the effect estimates for preterm birth were higher among those with greater cumulative dose (ORs=2.56, 4.02, and 4.60 for <2500, 2500–9999, and 10,000+ mgs respectively, compared to unexposed). There was also a higher risk of preterm birth among those who had been exposed to DES earlier in gestation (ORs=4.25, 2.76, 2.85, and 2.84 for <=7, 8–10, 11–14, and 15+ weeks at first exposure respectively). Among exposed women only, DES exposure early in gestation (<=7 weeks) was associated with a higher risk of preterm birth compared to late exposure (15+ weeks) (OR=1.50; 95% CI=1.15, 1.95).
DES was also associated with reduced birth weight. The mean difference in birth weight, adjusting for cohort and gestational age, was −105 grams (95% CI=−134, −76) (). Mean differences in birth weight were greater in the DESAD than in the Dieckmann cohort (−118 grams (95%CI=−151, −86) versus −52 grams (95%CI=−113, −10), respectively; p=0.08 for difference in estimates). The effect of DES on birth weight was slightly stronger among smokers (mean g=−153; 95%CI=−206, −101) than non-smokers (mean g=−103; 95%CI=−145, −61). Except for the large reduction in the effect estimates for birth weight with adjustment for gestational length (−188 grams unadjusted versus −105 grams adjusted), there was little evidence for confounding by other covariates in either cohort. In the subset of 4011 DESAD participants (79% of total cohort) with complete information on birth weight, gestational age, maternal age and smoking, and year of birth, DES exposure was associated with a 122 gram reduction in birth weight after controlling for gestational length (comparable to the estimate of −118 grams in the entire cohort before exclusion of those with missing data on potential confounders); this estimate was virtually the same (−126 grams) after additionally adjusting for maternal age, smoking, and year of birth of the index pregnancy. Among the 769 (95% of the total cohort) Dieckmann participants with complete information on birth weight, gestational length, and maternal age, the mean reduction in birth weight was 52 grams controlling for gestational length only and 53 grams with further control for maternal age at the index birth. (Year of birth was not included as a covariate in these models because of the small range in the Dieckmann cohort and maternal smoking was not included because of the large number of missing values.) In the subset of the DESAD cohort with dose information, birth weight did not appear to be related to cumulative total dose of DES, and there was little difference in birth weight according to membership in a high dose versus low dose cohort. Earlier exposure to DES during gestation also did not appear to be associated with greater reductions in birth weight.
Difference in mean birth weight and odds ratios (95%CI) for small for gestational age by DES exposure status, cohort, and dose and gestational age of first exposure to DES
DES exposure appeared to be related to the risk of being born SGA (), although the results were stronger in the DESAD (OR=1.75; 95% CI=1.37, 2.24) than the Dieckmann cohort (OR=1.26; 95% CI=0.83–1.90). The risk of SGA was not related to gestational age at first exposure to DES or to total dose, assessed either by estimation of low versus high dose cohort or by use of actual cumulative dose values in a subset. We assessed confounding by year of birth and maternal age and smoking in pregnancy within the DESAD cohort and found that the estimates changed very little (data not shown). The effect of DES on SGA among women whose mothers smoked in pregnancy was about the same (OR= 1.76; 95%CI=1.22, 2.52) as among those whose mothers did not smoke in pregnancy (OR= 1.90; 95%CI=1.30, 2.75).
The OR for prenatal DES exposure in relation to menarche ≤10 years was 1.41 (95% CI=0.97, 2.03), and for menarche ≤11 years, the OR was 1.16 (95% CI=0.97, 1.39) (). When early menarche was defined as ≤11 years, the results differed by cohort, with essentially null results in the Dieckmann cohort but a 25% increase in risk of early menarche in the DESAD cohort. Results were similar in the two cohorts using menarche ≤10 years as the outcome variable (). We tested for potential confounding in the DESAD cohort by adding maternal age at birth, smoking in pregnancy, and year of birth and found little change in the effect estimates for either menarche ≤10 years or ≤11 years (data not shown). For menarche ≤10 years, the effects were slightly stronger among those categorized as belonging to a high dose cohort (OR=1.50; 95%CI=1.02, 2.21) than those belonging to a low dose cohort (OR=1.24; 95%CI 0.81, 1.91), but there was essentially no difference in associations between the low and high dose cohorts when the outcome variable was menarche ≤11 years ().
Odds ratios (95% CI) for early menarche (defined as ≤10 and≤11 years old) by DES exposure status, cohort, and dose and gestational age of first exposure to DES (DESAD only)
The association between age at menarche and cumulative dose of DES appeared to be U-shaped, with some increase in early menarche in both the low (<2500 mg) and high (10,000+ mg) groups, and a slight reduction in risk of early menarche in those with moderate doses (total cumulative dose of 2500–9999 mg). Timing of first exposure to DES during gestation did not appear to affect the risk of early menarche, although first exposure later in gestation (15+ weeks) had slightly stronger effects than the other categories. With the exception of birth weight, there was little evidence that the effect of DES on age at menarche was modified by other variables. When the results were stratified by birth weight, there was a slightly reduced association of early menarche (≤11) among exposed women with birth weight <3000 grams (OR=0.91; 95% CI=0.63, 1.30), whereas the association was stronger among women with birth weights of 3000 grams or greater (OR=1.39; 95% CI=1.09, 1.79) (data not shown).
Similar results were found when we modeled age at menarche by individual year using Cox proportional hazards models (). DES-exposed women were slightly more likely to reach menarche at a younger age, but this association was evident only in DESAD (HR=1.09, 95% CI=1.02, 1.16), and not the Dieckmann (HR=0.97; 95%CI=0.82–1.14), cohort. There were no consistent patterns for dose and timing of exposure to DES in relation to menarcheal age in years.
Hazard ratios and 95% confidence intervals for the occurrence of menarche in DES-exposed compared to unexposed daughters, overall, by original cohort, and by dose and timing of first exposure (DESAD only)