Williams, M. A., Goldman, M. B., Mittendorf, R., & Monson, R. R. (1991). Subfertility and the risk of low birth weight. Fertility and Sterility, 56(4), 668-671. https://doi.org/10.1016/s0015-0282(16)54597-x
Williams MA, Goldman MB, Mittendorf R, Monson RR. Subfertility and the risk of low birth weight. Fertil Steril. 1991;56(4):668-671. doi:10.1016/s0015-0282(16)54597-x
Williams, Michelle A., et al. "Subfertility and the risk of low birth weight." Fertility and Sterility, vol. 56, no. 4, 1991, pp. 668-671.
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Delayed conception is linked to low birth weight in planned births
A Boston cross-sectional study of 3,622 married women with planned single births found that women who took over a year to conceive had nearly double the low birth weight risk. In unadjusted counts, low birth weight affected about 10 out of 100 of their babies. Among women who conceived sooner, the figure was about 5 out of 100.
Low birth weight: Over a year to conceive, 9.6 in 100; Conceived within a year, 4.9 in 100. Source: Williams MA et al., 1991, PMID 1915940.Study at a glance, cross-sectional study of 3,622 married women: Delayed conception was linked to nearly double the low birth weight risk. Source: Williams MA et al., 1991, PMID 1915940.
Key Findings
Of 3,622 nondiabetic married women with planned pregnancies, 644 took over a year to conceive and 2,978 conceived within a year.
Low birth weight (under 2,500 g) occurred in 62 of 644 women with delayed conception (9.6%) and 146 of 2,978 others (4.9%). Adjusted relative risk was 1.9 (95% CI, 1.3 to 2.8).
Term low birth weight (intrauterine growth retardation) occurred in 18 women with delayed conception (2.8%) and 51 others (1.7%). Adjusted relative risk was 2.3 (95% CI, 1.2 to 4.4).
Preterm low birth weight occurred in 29 women with delayed conception (4.5%) and 63 others (2.1%). Adjusted relative risk was 1.7 (95% CI, 1.0 to 3.1).
After adjustment, delayed conception was associated with a mean birth weight 93 g lower among all infants (95% CI, -46 to -140 g) and 58 g lower among term infants.
Interpretation
This cross-sectional study followed 3,622 nondiabetic married women with planned pregnancies, interviewed after delivery at one Boston hospital between 1977 and 1980, with answers combined with medical records. After adjusting for maternal age, race, smoking, parity and other factors, the association between delayed conception and low birth weight remained. The authors note that the data could not compare the different causes of delayed conception. The findings support larger studies of how time to conception affects birth weight.
RRM Context
Restorative reproductive medicine asks why conception is delayed. The authors suggest that hormonal, immune and cervical factors may interfere with fetal growth. A cause-based evaluation looks for factors of this kind.
Our editorial summary of this paper, not the article's abstract.
Abstract
Objective
We evaluated the association between subfertility and low birth weight infants.
Design
Women in this analysis participated in a cross-sectional investigation of maternal risk factors for adverse pregnancy outcomes.
Setting
Medical and obstetric history and life style information were obtained from women who delivered at the Boston Hospital for Women, 1977 to 1980.
PATIENTS,
Participants
Our analysis was restricted to nondiabetic married women who planned their pregnancies and subsequently delivered viable singletons (3,622). The 644 "subfertile" women (no conception during a year of unprotected intercourse) were compared with 2,978 "fertile" women (conception within 1 year).
Main Outcome Measures
The relative risk of low birth weight was estimated using the cumulative incidence risk ratio.
Results
After adjusting for confounding, the relative risk of delivering a low birth weight infant (less than 2,500 g) for subfertile women versus fertile women was 1.9 (95% confidence interval [CI], 1.3 to 2.8). The adjusted relative risk of delivering a term low birth weight (intrauterine growth retarded) infant was 2.3 (95% CI, 1.2 to 4.4).
Conclusions
In these data, subfertility is a predictor for low birth weight. The association may result from endocrinological, immunological, cervical, or other factors that interfere with optimal fetal growth.
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