Individualized birth length and head circumference percentile charts based on maternal body weight and height

ObjectivesMeasurement of birth length and birth head circumference is part of the newborn assessment. Both measurements aid in distinguishing between proportionate and disproportionate small and large for gestational age newborns. It had been shown that birth weight is related to maternal height and weight. This study aims to analyze birth length and birth head circumference percentiles based on maternal stature.MethodsThis observational study analyzed birth length and birth head circumference percentiles of 2.3 million newborns stratified by maternal height and weight from the first obstetric assessment. Percentiles were calculated for sex and 22–43 gestational weeks for all infants. Eighteen subgroups based on six maternal height and three weight strata were defined and percentiles calculated from 32 to 42 gestational weeks using GAMLSS package for R.ResultsNewborns of mothers with height <158 cm and weight <53 kg (short stature) had a rate of preterm birth of 9%, compared to 5% in the tall stature group (height >177 cm, weight >79 kg). Small stature mothers were 1.7 years younger. Birth length differed by several centimeters for the same percentiles between groups of short and tall stature mothers, whereas birth head circumference differed up to 1.2 cm. The largest deviation of birth length was between the 97th percentiles. For male newborns born at term, birth length at the 97th percentile differed by 3.2 cm, at the 50th percentile by 2.7 cm and at the third percentile by 2.5 cm.ConclusionsBirth length and birth head circumference are related to maternal height and weight. To more completely assess newborns, the maternal size should be considered.

How many cubs can a mum raise? Maternal age and size influence litter size in polar bears

Life history theory predicts that females’ age and size affect the level of maternal investment in current reproduction, balanced against future reproductive effort, maintenance and survival. Using long-term (30 years) individual data on 231 female polar bears (Ursus maritimus), we assessed age- and size-specific variation on litter size. Litter size varied with maternal age, younger females had higher chances of losing a cub during their first months of life. Results suggest an improvement of breeding abilities early in life due to experience with subsequent reproductive senescence. Litter size increased with maternal size, indicating that size may reflect individual quality. Heterogeneity was observed among the largest females, suggesting that large size comes at a cost. Maternal traits and environmental conditions may act together to influence reproductive success.