The impact of the COVID-19 lockdown on birthweight among singleton term birth in Denmark

{"background": "The COVID-19 pandemic had both direct effects from SARS-CoV-2 infection and indirect effects from mitigation strategies on maternal and fetal health. Denmark implemented a strict nationwide lockdown from March 12 to April 14, 2020, restricting social interaction, workplace attendance, and travel. Prior studies had shown reduced rates of extremely preterm and extremely low birthweight births during lockdowns, without increases in stillbirth or perinatal death. Birthweight and size-for-gestational-age are established surrogate markers of intrauterine conditions, and any detectable changes in term birthweight would indicate that lockdown measures affected prenatal growth, potentially impacting long-term health outcomes including hypertension, chronic disease, and metabolic syndrome.", "methods": "The authors conducted a nationwide register-based cohort study using data from the Danish Neonatal Screening Biobank, which has near 100% uptake as neonatal screening is mandatory within three days of birth. They included 27,870 live singleton term infants (gestational age 37+0 to 41+6 weeks) born between March 12 and April 14 across 2015\u20132020. Births with missing birthweight/gestational age data or values beyond 5 SD of the mean for each gestational week and sex were excluded (3.6% of term pregnancies). Gestational age was calculated from first-trimester ultrasound. SGA was defined as birthweight <10th percentile and LGA as >90th percentile at each completed week by sex, using INTERGROWTH-21 international standards. A secondary analysis used population-based 5th and 95th percentile cutoffs. Multivariable linear regression assessed associations of lockdown period, gestational length, and sex with birthweight. Multinomial and logistic regression were used for xGA categories. Analyses used R version 4.2.0.", "key_results": "No significant temporal trends in birth rate, sex ratio, or gestational age distribution were noted during 2015\u20132019 (\u03c7\u00b2 p = 0.71). The proportion of births in gestational weeks 40 and 41 was significantly higher during lockdown at 59.7% versus 57.7% (95% CI 57.5\u201357.9) in previous years. Crude mean birthweight increased by 26.4 g (95% CI 11.15\u201341.05) during lockdown compared to the previous five years. After adjustment for sex and gestational age, the increase was 16.9 g (95% CI 2.80\u201330.75). Stratified analysis showed birthweight decreased by 33.9 g in weeks 37\u201338 (95% CI -68.53 to 0.69) but increased by 26.3 g in weeks 39\u201341 (95% CI 11.33\u201341.31), indicating the increase was driven by later term births. The LGA proportion increased for both sexes: girls 28.9% vs 26.7% (95% CI 25.1\u201328.3), boys 29.8% vs 26.8% (95% CI 25.7\u201328.0). Adjusted OR for LGA using INTERGROWTH-21 was 1.13 (95% CI 1.05\u20131.21); using population-based 95th percentile cutoffs, OR was 1.16 (95% CI 1.01\u20131.33). SGA showed no significant change (aOR 1.00, 95% CI 0.82\u20131.22 using INTERGROWTH-21). No temporal trend in LGA or SGA was observed during 2015\u20132019 that could explain the lockdown-associated increase.", "clinical_implications": "The 26.4 g crude birthweight increase during lockdown approximates less than one day of intrauterine growth in term infants but is roughly equivalent to about 10% of the effect of not smoking during pregnancy. The increase may reflect beneficial factors (improved maternal rest, reduced work-related stress, better nutrition, lower infection burden) or potentially pathologic mechanisms (increased gestational weight gain, dysregulated gestational diabetes, changes in induction or delivery practices). The rise in LGA proportion is clinically concerning because LGA predisposes to delivery complications, neonatal hypoglycemia, and later obesity and metabolic syndrome. Possible explanations include increased maternal BMI and gestational weight gain, postponement or suspension of labor inductions reducing iatrogenic early births, reduced maternal stress from staying home, decreased work-related physical strain, or changes in antenatal care delivery. The LGA increase should be monitored carefully during future pandemic mitigations. Study strengths include the large national sample with near-complete ascertainment, real-time mandatory data collection, and validation using both international and population-based references. Limitations include exclusion of stillbirths and early postnatal deaths, gestational age reported in completed weeks rather than days, and lack of maternal data on BMI, gestational weight gain, pregnancy complications, induction, and delivery mode, which precluded causal inference."}