Socioeconomic status affects the prevalence, but not the perinatal outcomes, of in vitro fertilization pregnancies.

STUDY QUESTION: Does maternal socioeconomic status (SES) confound or modify the association between IVF and perinatal outcome among singleton births? SUMMARY ANSWER: There were substantial socioeconomic differences in the frequency of IVF pregnancies, but maternal SES was not associated with the outcome of IVF pregnancies. WHAT IS KNOWN ALREADY: The use of IVF is associated with SES. Additionally, women with lower SES tend to have an increased risk of adverse perinatal outcomes such as preterm birth and small for gestational age birth. STUDY DESIGN, SIZE, DURATION: We conducted a population-based cohort study using the Finnish Medical Birth Register (2006-2010). PARTICIPANTS/MATERIALS, SETTING,
METHODS: We analyzed the total population of singleton births in Finland (n = 291 004) and then compared the unadjusted and adjusted incidences of adverse perinatal outcomes for singleton births after IVF (n = 5647) and non-IVF pregnancies (n = 285 357) in relation to SES. MAIN RESULTS AND THE ROLE OF CHANCE: SES did not confound or modify the association between IVF and perinatal outcomes after adjustments for age, parity, smoking, gestational diabetes, maternal diabetes and pre-eclampsia. However, the prevalence of IVF pregnancies increased with SES; on average 1.9% of singleton infants were born after IVF pregnancies, while the corresponding percentages were 3.2 and 1.2% for the highest and lowest SES strata, respectively. IVF was statistically significantly associated with 1.27-, 1.49-, 1.63-, 1.47-, 1.35-, 1.40-, 4.97- and 1.14-fold higher incidences of admission to a neonatal unit, stillbirth, preterm birth, low birthweight, low Apgar scores (<7 at 5 min), Cesarean section, placenta previa and major congenital anomaly, respectively. Irrespective of the SES group, women who became pregnant through IVF were older and more often nulliparous and non-smokers compared with women with non-IVF pregnancies. LIMITATIONS, REASONS FOR CAUTION: The occupation of 22% of the women was unknown and that of a further 25% did not match any of the criteria for our SES strata. Additionally, infertility is a problem for couples but the definition of SES in this study was based only on the mother's occupation at the time of birth. WIDER IMPLICATIONS OF THE
FINDINGS: The prevalence of IVF-conceived pregnancies was highest among the highest SES group, but SES did not confound the perinatal outcomes of IVF pregnancies after adjusting for background factors. However, the magnitude of risks associated with the IVF technique itself may be more significant than previously thought. STUDY FUNDING/COMPETING INTEREST(S): None of the authors received any funding specifically for this study, and we have no competing interests.