Trends of change in the individual contribution of risk factors for small for gestational age over more than 2 decades

Purpose: Over the past years, the prevalence of various risk factors for small for gestational age (SGA) neonates has changed. Little is known if there was also a change in the specific contribution of these risk factors to the prevalence of SGA. We aim to identify trends in the specific contribution of various risk factors for SGA by observing their odds ratios (ORs) throughout different time periods. Methods: A nested case–control study was conducted. The ORs for selected known risk factors for SGA occurring in three consecutive 8-year intervals between 1988 and 2014 (T1 – 1988–1996; T2 – 1997–2005; T3 – 2006–2014) were compared. Data were retrieved from the medical centre’s computerized perinatal database. Multivariable logistic regression models were constructed and ORs were compared to identify the specific contribution of independent risk factors for SGA along the study period. Results: During the study period, 285,992 pregnancies met the study's inclusion criteria, of which 15,013 (5.25%) were SGA. Between 1988 and 2014, the incidence of SGA increased from 2.6% in 1988 to 2.9% in 2014. Using logistic regression models, nulliparity, maternal age, gestational age, hypertensive disorders of pregnancy, oligohydramnios and pre-gestational diabetes mellitus were found to be independently associated with SGA. While the adjusted ORs (aOR) of hypertensive disorders of pregnancy and pre-gestational diabetes mellitus had increased, aORs for nulliparity, maternal age and gestational age had remained stable over time. Oligohydramnios had demonstrated a mixed trend of change over the time. Conclusion: In our study, the specific contribution of factors associated with SGA had changed over time. Having a better understating of the changes in the specific contribution of different risk factors for SGA may enable obstetricians to provide consultations.