Methods pregnancy dating
Although often treated as term, late preterm infants more commonly present with prematurity-related morbidity such as hyperbilirubinemia, respiratory distress syndrome (RDS) of the newborn, transient tachypnea of the newborn, interventions to support breathing, and readmissions for hospital care .
After changing the pregnancy dating method, male infants born early term had, in relation to female infants, higher odds for pneumothorax (Cohort ratio [CR] 2.05; 95 % confidence interval [CI] 1.33–3.16), respiratory distress syndrome of the newborn (CR 1.99; 95 % CI 1.33–2.98), low Apgar score (CR 1.26; 5 % CI 1.08–1.47), and hyperbilirubinemia (CR 1.12; 95 % CI 1.06–1.19), when outcome was compared between the two time periods.In a study by Skalkidou et al., increased mortality and morbidity in post-term female infants in relation to male infants was seen after US was introduced in Sweden as the method for assessing GA .This increase in mortality and morbidity can reflect the fact that girls born post-term may be more mature than their US-based GA indicates, as their EDD was moved forward in time because of their smaller size at the time of ultrasound pregnancy dating.Since then, the use of first-trimester US has increased gradually.Our study population consisted of two cohorts including all singleton births in Sweden, with valid birth dates for both mother and infant, from 1973 to 1978 (GA assessment based on the LMP date) and from 1995 to 2010 (GA assessment by US).According to this hypothesis, male fetuses could be less mature than the US-based GA estimate, since the approximation of GA from fetal size used during ultrasound dating would not consider size differences.
In Sweden, a second trimester scan, using the biparietal diameter (BPD)-measurement for pregnancy dating, is typically performed around gestational week 18 at what time the mean difference (male vs. An introduced bias in the GA estimate, due to size difference by fetal sex at the time of pregnancy dating, would be hypothesized to affect clinical management and neonatal outcomes in the late preterm and early term period.
These were: pneumothorax P25 (ICD-10), 7702 (ICD-9), 77620, and 77625 (ICD-8); RDS P22.0 (ICD-10), 769 (ICD-9), and 7761 (ICD-8); other respiratory conditions such as P22.1, P22.8, P22.9, P28.3, P28.4 (ICD-10), 7706, 7708 (ICD-9), 77629, 77699, and 77680 (ICD-8); hyperbilirubinemia P55, P57, P58, P59 (ICD-10), 7730, 7731, 7732, 7734, 7735, 774 (ICD-9), 774, 775, and 77893 (ICD-8) .
For the purposes of this study, infants were classified into three groups: those born from 39 weeks 0 days to 40 weeks 6 days (273–286 days, designated midterm); from 37 weeks 0 days to 38 weeks 6 days (259–272 days, designated early term); and from 35 weeks 0 days to 36 weeks 6 days (245–258 days, hereby referred to as late preterm).
By contrast, from 1995 on, nearly all clinics based EDD assessment on US biometry and documented the EDD-US in the MBR.
Routine US scanning has been offered to all pregnant women since 1990, and more than 95 % of the women accept this offer .
We compared prevalence of outcomes between sexes in a time period when LMP was used as the only method for dating pregnancies (1973–1978) and similarly the prevalence of outcomes were compared between sexes after US was introduced as the method for dating pregnancies (1995–2010).