Genetic Factors Influencing Birth Weight

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Genetic Factors Influencing Birth Weight

Date of Content: March 14, 2024
Written by: Avanthika Nityanand
Reviewed by: Maarit Tiirikainen, PhD


Birth weight (BW) is the first weight of a newborn, measured shortly after birth. This metric is crucial for assessing the newborn’s health status and potential healthcare needs. Typically recorded in kilograms or pounds, birth weight is a pivotal indicator of the baby’s growth and development in the womb and can signal various health conditions.

An optimal birthweight reflects adequate nutrition and fetal development during pregnancy, which is vital in determining a child’s immediate and long-term health outcomes. High or low birth weights can lead to different health challenges, making this measurement essential for neonatal care and future health planning.

Birth weight

What is Considered Low Birth Weight?

If the weight at birth is less than 2,500 grams (5 pounds, 8 ounces), it is termed low birthweight (LBW).  This condition can result from premature birth, where the infant is born before the 37th week of pregnancy, or from intrauterine growth restriction (IUGR), where the growth of the fetus is limited. 

LBW is a significant concern for healthcare providers as it is associated with an increased risk of infant mortality and various developmental and health problems later in life, including cardiovascular diseases, diabetes, and respiratory conditions. To improve survival rates and health outcomes of newborns, managing and preventing LBW is a priority in neonatal care.

Is Birth Weight Hereditary?

Both hereditary (genetic) and environmental factors influence birth weight. The genetic component is evident in the observed similarity in birthweight among relatives. An early study observed that birth weights of parents explain 2% of the variance in birth weights of sons and 5% in daughters.

A 2021 meta-analysis found a significant positive correlation between the BW of twins and 150 previously identified genetic variants linked to singleton BW. Furthermore, a strong genetic correlation was observed between BW in twins and singletons, with a genetic correlation (rg) value of 0.92, indicating a similar genetic architecture for BW in both groups.

Genetic Factors Influencing Birthweight

Several genetic factors can influence birth weight by affecting fetal growth and development. These factors include gene variations related to growth factors, metabolism, and the placenta’s development and function. 

A 2018 GWAS analyzed data from up to 86,577 women of European descent, part of the Early Growth Genetics (EGG) Consortium and the UK Biobank; researchers identified maternal genetic variants at ten loci (including MTNR1B, HMGA2, and CYP3A7) that are associated with offspring birth weight.


MTNR1B is involved in the physiological regulation of insulin secretion and glucose homeostasis. It has implications for metabolic control within the body. Variants in the MTNR1B gene are associated with altered fasting glucose levels, increased risk of type 2 diabetes, as well as gestational diabetes. Research has also shown a link between genetic variations in MTNR1B and differences in birth weight, suggesting that the gene may influence fetal growth through its effects on maternal glucose metabolism and possibly other pathways related to melatonin signaling.

A 2015 meta-analysis of 11 GWAS involving 19,626 women of European descent pinpointed 18 SNPs for further examination in up to 13 additional studies comprising 18,319 women. One SNP within the MTNR1B gene (rs10830963) reached genome-wide significance, demonstrating a notable association with birth weight and known links to fasting glucose levels, type 2 diabetes, and gestational diabetes from previous studies. Specifically, each copy of the rs10830963 G-allele, associated with higher fasting glucose, was linked to a 31g increase in offspring birth weight. 


The HMGA2 (High Mobility Group AT-hook 2) gene encodes a protein that belongs to the high mobility group (HMG) of non-histone chromosomal proteins. HMGA2 is particularly notable for its involvement in developmental processes. Variants in this gene have been associated with human height, suggesting a significant role in growth. HMAGA2 has been linked to birth weight and affects adipose (fat) tissue mass, indicating its relevance in prenatal development and metabolic regulation.

The SNP rs1351394 within the HMGA2 gene, known for its role in encoding the high mobility group-A2 protein, was associated with birth weight in Ladakhi offspring. High mobility group (HMG) proteins are critical nuclear components that bind to DNA, altering chromatin structure and thus regulating gene expression. The HMGA2 gene, in particular, has been linked to variations in height and birth weight among lowland populations and differences in adipose (fat) mass in pigs. It positions HMGA2 as a biologically plausible candidate for influencing these traits also in humans, highlighting its significance in genetic studies focused on physical development.

However, genetics alone does not influence birth weight. Your genes interact with environmental and maternal factors during pregnancy. The heritability of birthweight suggests that while genetics plays a role, it is part of a complex interplay of factors that affect fetal development.

Beyond the interesting findings of genetic variants in biologically relevant genes, also so called Polygenic Risk Scores (PRS) can be developed for the association between SNPs and Birth Weight. The PRS embrace the polygenic nature common to many human traits. The LifeDNAs SNP signature for Birth Weight is based on a PRS that includes over 6,000 SNPs (top 15 shown) , derived from a large study involving over 280,000 participants.

Non-Genetic Factors Influencing Birth Weight

Non-genetic factors significantly influence birth weight, a crucial determinant of newborn health and future development. These factors vary widely and include maternal, environmental, and lifestyle elements. Understanding these can help manage or mitigate risks associated with low or high birth weights. Here are some notable non-genetic factors:

  • Maternal Health and Nutrition: The mother’s health and nutritional status before and during pregnancy are critical. Malnutrition or poor diet can lead to low birth weight, while excessive weight gain can result in a higher birth weight. Conditions like gestational diabetes and hypertension also impact birth weight.
  • Prenatal Care: Regular prenatal check-ups help monitor the health of both the mother and the fetus. Early detection and management of potential issues can influence birth weight outcomes.
  • Maternal Age: Teen mothers or those over 35 are at higher risk of having babies with low or high birth weight, respectively, due to various physiological and health-related factors.
  • Lifestyle Factors: Smoking, alcohol consumption, and drug use during pregnancy lead to reduced birth weight and adverse health outcomes for the newborn.
  • Environmental Exposures: Exposure to pollutants, toxins, and certain chemicals during pregnancy can affect fetal growth and lower birth weights.
  • Socioeconomic Status: Lower socioeconomic status is often associated with reduced access to quality healthcare, nutrition, and higher stress levels, all of which can influence birth weight.
  • Stress and Emotional Well-being: High-stress levels and poor emotional well-being during pregnancy can negatively impact birth weight, possibly due to hormonal imbalances and other physiological changes.
  • Physical Activity: Moderate physical activity during pregnancy is beneficial, but excessive or strenuous exercise might adversely affect birth weight.
  • Multiple Pregnancies: Twins or multiple births often have lower birth weights compared to single-birth pregnancies due to space and resource constraints in the womb.
  • Gestation Period: The length of the pregnancy significantly influences birth weight; preterm births usually result in lower birth weights, while post-term births might lead to higher birth weights.

What New Mothers Can Do to Ensure Healthy Birth Weight

New mothers can take several proactive steps to promote a healthy birth weight for their newborns. These include securing regular prenatal care to monitor the baby’s development, adopting a healthy diet rich in essential nutrients, and avoiding harmful substances like tobacco, alcohol, and illicit drugs. 

Managing chronic health conditions and seeking appropriate treatment for pregnancy-related issues are also vital. Additionally, staying active within healthcare provider recommendations can support healthy fetal growth. Educating themselves about pregnancy and newborn care and utilizing available resources and support systems can enhance the chances of a healthy birthweight and a positive start to their child’s life.

About the LifeDNA Report on Birth Weight

The LifeDNA Wellness Report includes Birth Weight Trait, delving into genetics’ substantial impact on fetal growth and birth weight. The report also notes that fetal genes may counterbalance maternal genetic influences, sometimes resulting in lower birth weight. It highlights the intricate genetic dance that determines birth weight, suggesting that the interplay is far from straightforward and that multiple genetic and environmental factors influence it.

The significance of understanding these genetic influences extends beyond birth. The genetic markers associated with birth weight are indicators of neonatal health. They can serve as crucial predictors for future wellness outcomes. Identifying these genetic factors opens up the possibility of personalized health insights from an early stage, allowing for targeted interventions that could mitigate health risks later in life.



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*Understanding your genetics can offer valuable insights into your well-being, but it is not deterministic. Your traits can be influenced by the complex interplay involving nature, lifestyle, family history, and others.

Our reports and suggestions do not diagnose or treat any health conditions or provide any medical advice. Consult with a healthcare professional before making any major lifestyle changes or if you have any other concerns about your results.