Perinatal outcomes of singleton siblings: the effects of changing maternal fertility status

The objective of this study was to evaluate the effect of changing fertility status on perinatal outcomes of singleton siblings, conceived with and without assisted reproductive technology (ART). A longitudinal cohort study of Massachusetts resident women having two consecutive singleton births during 2004-2010 was performed. Women were classified as ART (A), subfertile (S), or fertile (F) and categorized by their fertility status in each birth as A-A, A-S, S-A, S-S, F-A, F-S, and F-F. Within categories, adjusted mean birthweights, gestations, and birthweight Z scores were estimated with linear generalized estimating equations. Risks of low birthweight (LBW, < 2500 g), preterm birth (PTB, < 37 weeks), and placental complications were modeled using logistic regression by fertility status as adjusted odds ratios (AORs) and 95 % confidence intervals (CIs). Birthweights in second pregnancies averaged 74-155 g higher, except for births to F-A women, who averaged -16 g lower. Most women had a reduction in length of gestation in their second pregnancies, with F-A women having the largest decline (-0.5 weeks). In first birth models, the risks for LBW and placental complications were increased for subfertile (AOR 1.39 [1.07-1.81] and 1.97 [1.33-2.93], respectively) and ART women (AOR 1.58 [1.29-1.93] and 3.40 [2.64-4.37], respectively). Second birth models showed increased risks for ART births of LBW (AOR 3.13 [2.19-4.48]) and placental complications (AOR 2.45 [1.56-3.86]) and greater risks of PTB for both ART (AOR 2.37 [1.74-3.23]) and subfertile women (AOR 1.47 [1.02-2.13]). Declining fertility status, with and without assisted reproductive technology treatment, is associated with increasing risks for adverse outcomes, greatest for women whose fertility status declined the most.