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.