Risks of adverse pregnancy and birth outcomes according to maternal age and inter-pregnancy interval

Project number: 
Approval date: 
Thursday, March 3, 2016
Principal Investigator: 
Harvard Medical School
Funding Agency: 
Datasets requested: 
Medical Services Plan (BC Ministry of Health)
Deaths (BC Vital Statistics Agency)
Hospital Separations (BC Ministry of Health)
Income band (Statistics Canada)
Consolidation - demographic (Ministry of Health)
Perinatal Services BC
consolidation - census geocodes
Research objective: 

Specific Aim 1: Estimate the absolute risk of 14 adverse pregnancy and birth outcomes according to 1-year increments of maternal age at pregnancy. We will estimate the absolute risks of preeclampsia, gestational diabetes, spontaneous preterm delivery, indicated preterm delivery, cesarean delivery, spontaneous vaginal delivery, severe postpartum hemorrhage, severe maternal morbidity, in-hospital maternal mortality, stillbirth, small for gestational age birth (SGA), neonatal intensive care unit (NICU) stay >=48 hours, neonatal mortality, and a composite maternal-perinatal adverse outcome index according to maternal age at first pregnancy in 1-year increments. Findings will inform prepregnancy counseling and public health messaging.

Aim 1b. Determine how sensitive previous findings are to exposure and referent group definitions. We will conduct analyses using each dichotomous cutoff (e.g., >=35 or >=40) and each referent group (e.g., 20-24,

Specific Aim 2: Use a causal framework to estimate the proportion of the effect of age at pregnancy on adverse birth outcomes that would be eliminated if multiple pregnancies and adverse complications of pregnancy were completely prevented. We propose to conduct a mediation analysis to identify the extent to which the effect of age at first pregnancy on the risk of adverse outcomes (cesarean delivery, spontaneous and indicated preterm delivery, severe postpartum hemorrhage, severe maternal morbidity, maternal mortality, stillbirth, SGA, NICU stay >=48 hours, and newborn death) is mediated by preeclampsia, gestational diabetes, and multiple gestations.

Specific Aim 3: Identify the optimal inter-pregnancy interval for women aged 30 or older. We will compare the outcomes of pregnancies to women aged 30 or older according to different inter-pregnancy intervals. We will examine whether the recommended inter-pregnancy interval for the general population (18-23 months between delivery and subsequent pregnancy) is applicable to this specific population or whether specific guidelines targeting an older population are necessary. We will examine separately nulliparous and parous women in this age group, as parity may modify these effects. To date, this population has little evidence to guide timing of subsequent pregnancies. These results will fill this knowledge gap, with immediate application to clinical practice, practice guidelines, and public health communication.

Page last revised: December 5, 2017