Introduction
Preterm birth (PTB) is a leading cause of neonatal morbidity and mortality.1 The rate of PTB has increased in many locations,1,2 predominantly because of increasing rates of provider-initiated PTB and increased access to Infertility treatment associated with high rates of multiple pregnancy.1 Nonetheless, singleton pregnancy after infertility treatment is also associated with PTB.3 It is unclear whether the baseline infertility diagnosis, type of infertility treatment,4 or pregnancy complications associated with infertility treatment,5 contribute differentially to the increased risk of PTB.6Furthermore, others have reported that infertility without infertility treatment (i.e subfertility), may be associated with PTB.7,8
PTB is not comprised of a single entity, but different subtypes.1 About 30–35% of PTB are provider-initiated — otherwise termed “iatrogenic” or “indicated”— with rates as high as 50% in many high-income countries.1,9 Provider-initiated PTB occurs through induction of labour or prelabour caesarean delivery, typically owing to a maternal and or fetal indication.1 The other 50%-70% of PTB are spontaneous, after onset of spontaneous preterm labour or preterm premature rupture of the membranes (PPROM).1 Provider-initiated PTB is associated with twice the risk of neonatal mortality and morbidity compared with spontaneous PTB.2,10,11
Most studies examining PTB in relation to mode of conception have assessed PTB as a single entity. There are a lack of data about the role of subfertility and non-invasive infertility treatment (Ovulation induction [OI], or Intrauterine Insemination [IUI]) on PTB subtypes. Studies have reported an increased risk of spontaneous PTB following Invasive- infertility treatment, namely, In VitroFertilization (IVF) and Intracytoplasmic Sperm Injection (ICSI).12 Risk factors for both spontaneous and provider-initiated PTB include non-Caucasian ethnicity, previous preterm birth, and lower socioeconomic status, among others.13Access to infertility treatment is influenced by sociodemographic characteristics, including ethnicity, income, education, smoking and higher body mass index (BMI). 14-16 To account for these factors, previous studies used matching or stratification.12 Of note, propensity score methods have more recently been used to reduce the effects of confounding in observational studies that aim to estimate treatment effects.17
Understanding the association between PTB subtypes in women with subfertility and those who receive infertility treatment may help improve strategies for PTB prevention. Accordingly, this population-based cohort study evaluated the association between mode of conception and risk of PTB, including, spontaneous and provide-initiated PTB.