Multiple births and maternal mental health from pregnancy to 5 years after birth: a longitudinal population-based cohort study

Background: There is a lack of population-based studies on multiple births and maternal mental health. Having a high-risk pregnancy by bearing two or more children is a stressful life event, and the challenges of parenting two or more children probably also lead to a high level of parental stress. There are a few results on multiple births and maternal mental health from studies on in vitro fertilization samples. The only previous cohort study on multiple birth and maternal mental health included a single measure of depressive symptoms at 9 months postpartum. We aim to estimate the relative risk for depression and anxiety after multiple birth in a population-based prospective cohort study while adjusting for factors prior and subsequent to fertilization. Methods: We used data from 87,807 pregnancies included in the Norwegian Mother and Child Cohort study. Information on multiple birth was retrieved from the Norwegian Medical Birth Registry, and maternal mental health was assessed at 17th and 30th week of gestation and 0.5, 1.5, 3, and 5 years postpartum. There were 1,842 plural births included in the study (i.e. 1,821 twin births and 21 higher order births). We predicted maternal mental health at each time point, subsequently adjusting for 1) factors prior to fertilization (e.g. maternal age and in vitro fertilization); 2) factors during pregnancy (e.g. hypertensive states); 3) factors at delivery (e.g. cesarean section); 4) child-related postnatal complications (e.g. intracranial hemorrhage); and 5) concurrent depression or anxiety after pregnancy. Results: Adjusted for antecedents of plural birth, mothers expecting a plural birth had a normal risk for anxiety (RR=1.05; 95% CI 0.92-1.20) and depression (RR=1.02; 95% CI 0.89-1.16) at 17th week of gestation. However, plural birth was associated with maternal depression at 1.5, 3, and 5 years postpartum and maternal anxiety at 3 years postpartum. The trend was for the association to increase across time, and mothers of multiplets had a significant higher risk for depression at 5 years (RR=1.77; 95% CI 1.33-2.35). Fully adjusted the RR for depression was 1.51 (95% CI 1.10-2.08). By adjusting depression for concurrent anxiety, and vice versa we found the effect of multiple pregnancy to be specific to depression and not anxiety. Conclusions: Mothers expecting multiplets have normal mental health during pregnancy. After birth there is an increasing risk for depression up to 5 years of age. Our findings indicate that more is simply more, and mothers of multiplets have need for additional support several years postpartum