P-447 Gestational weight gain in relation to time-to-pregnancy and conception by assisted reproductive technology
Authors: Laursen A S D , Mikkelsen E M , Mitter V , Magnus M C 
Published: June 2023

Abstract

Study question
Does the gestational weight gain trajectory differ across levels of time-to-pregnancy (TTP) for spontaneously conceived pregnancies and pregnancies conceived by assisted reproductive technology (ART)?

Summary answer
Women with ART pregnancies had lower weekly weight gain during the third trimester compared with women with spontaneous conceptions with TTP ≤3.

What is known already
Studies suggest that both prolonged TTP and conception by ART may increase the risk of pregnancy complications and affect perinatal outcomes such as birthweight. Suboptimal gestational weight gain might further increase the risk of adverse pregnancy outcomes. However, it remains unclear whether there may be differences in gestational weight gain according to TTP and ART, which contribute to the subsequent risk of adverse pregnancy outcomes.

Study design, size, duration
We studied 69,121 singleton planned pregnancies contributed by 60,847 women participating in the Norwegian Mother, Father and Child Cohort Study. Participants completed questionnaires at 15 weeks’ gestation (study entry), 30 weeks’ gestation, and six months postpartum on sociodemographic, reproductive, and behavioral factors. Participants reported their TTP, and up to four weight measurements and corresponding gestational age from preconception through delivery. We identified use of ART in the Medical Birth Registry of Norway.

Participants/materials, setting, methods
We fitted gestational weight gain trajectories using mixed-effects linear regression models and included an interaction term between time (gestational weeks) and the exposure groups, TTP ≤3 (reference); TTP 4-6; TTP 7-11, TTP ≥12 months, and ART, to assess differences across levels of TTP and conception by ART. The analyses were adjusted for maternal age at start of pregnancy, pre-pregnancy height, educational attainment, pre-pregnancy smoking, parity, and gestational age at birth.

Main results and the role of chance
The adjusted average weekly weight gain was -15g (95% CI: −19; −12) during the first trimester, 620g (95% CI: 615; 624) during the second trimester, and 491g (95% CI: 489; 494) during the third trimester. When we compared differences in average weekly weight change during the first trimester, we observed little difference between the exposure groups. During the second trimester, compared with TTP≤3 months women with TTP 4-6 months, TTP 7-11 months or TTP ≥12 months gained on average 7g (95% CI: −18; 3), 19g (95% CI: −33; −5) and 15g (95% CI: −29; −1) less per week, respectively, whereas women with ART pregnancies gained 11g more per week (95% CI: −13; 34). However, the results for TTP 4-6 and ART pregnancies were imprecise. During the third trimester, average weekly weight gain did not differ according to TTP for spontaneous conceptions, while women who conceived after ART gained 35g (95% CI: −49; −22) less than women with TTP≤3 each week.

Limitations, reasons for caution
Because TTP and gestational weight gain were self-reported, non-differential misclassification may have influenced our results.

Wider implications of the findings
Decelerated weight gain during the third trimester in ART pregnancies compared with women who conceived spontaneously within 3 months might be associated with adverse pregnancy outcomes. Although our findings are imprecise and need to be replicated, monitoring gestational weight gain trajectories might support identification of pregnancies at increased risk.

Trial registration number
Not applicable