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).
Most pregnancies last around 40 weeks (or 38 weeks from conception), so typically the best way to estimate your due date is to count 40 weeks, or 280 days, from the first day of your last menstrual period (LMP).
Furthermore, postponing the date of estimated delivery by 7 days by US is associated with birth of SGA infants , increased risk of stillbirth, low Apgar score, and neonatal death .The reported sex differences in early fetal growth [7, 8] can be used as one example among many other variables possibly affecting the accuracy of US-based estimation of GA.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.But if your cycle is irregular, the LMP method may not work for you.
Because a reliable estimated date of delivery (EDD) is important, you and your practitioner can use your conception date instead if you remember it. There are more than 250,000 assisted reproductive technology cycles performed each year in the United States, resulting in about 77,000 or more babies born a year, according to the Centers for Disease Control and Prevention (CDC).
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 .
Our hypothesis was that a change in the method of dating pregnancy might have led to an increased risk for prematurity-related adverse outcomes among male infants in relation to female infants by introducing a misclassification bias due to sex differences in early growth.
As expected, adverse outcomes were lower in the later time period, but the reduction in prematurity-related morbidity was less marked for male than for female infants.
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.
Talk to your practitioner if you have any questions or concerns.