Data on the study population were cross-tabulated by infant sex, GA, and the two time periods (1973–19–2010).
As a first step, rates of adverse outcomes per 1000 live births were calculated according to infant sex, GA, and the studied period.
This cohort study included data on 1,314,602 births recorded in the Swedish Medical Birth Register.
Before 1980, fewer than 5 % of hospitals practiced US scanning.
The aim of this study was to compare rates of adverse prematurity-related outcomes in early term and late preterm male infants in relation to their female counterparts, between a time period, when pregnancy dating was based on the LMP, and a time period when ultrasound was used for pregnancy dating, in order to assess the dating method’s influence on prematurity-related adverse outcomes by fetal sex.
In this study, we used data on 1,314,602 births in Sweden to compare adverse outcomes related to prematurity between male and female infants by method of pregnancy dating (US or from LMP).
Information was retrieved on GA at delivery (based on LMP date and US assessment, respectively), the level of the hospital, maternal age, parity, infant sex, Apgar score , any neonatal deaths, and diagnoses of adverse outcomes related to late prematurity.
Diagnoses that allowed comparison between the ICD versions and with higher incidence among premature infants were chosen.