Birth weight is the first weight of your baby, taken just after he or she is born. A low birth weight is less than 2.5kg (5.5 pounds) while a high birth weight is more than 4kg (8.8 pounds). The birth weight of a baby is notable because very low birth weight babies are 100 times more likely to die compared to normal birth weight babies. A low birth weight baby can be born too small, too early (premature), or both. This can happen for many different reasons. They include health problems in the mother, genetic factors, problems with the placenta, and drug use by the mother. Some low birth weight babies may be more at risk for certain health problems. Some may become sick in the first days of life or develop infections. Others may suffer from longer-term problems such as delayed motor and social development or learning disabilities. High birth weight babies are often big because the parents are big, or the mother has diabetes during pregnancy. These babies may be at a higher risk of birth injuries and problems with blood sugar (MedlinePlus, 2020).
Determinants of Birth Weight of Newborns
Different factors determine the birth weight of newborns, notable among them are as shown below:
There are two genetic loci that have been strongly linked to birth weight, ADCY5 and CCNL1, as well four that show some evidence (CDKAL1, HHEX-IDE, GCK, and TCF7L2). The heritability of birth weight ranges from 25-40 %.There is a complex relationship between a baby’s genes and the maternal environment that the child is developing in. Foetal genes influence how the fetus grows in utero, and the maternal genes influence how the environment affects the growing fetus (Yaghootkar & Freathy, 2012).
Stressful events have been demonstrated to produce significant effects on birth weight. Those mothers, who have stressful events during pregnancy, especially during the first and second trimester, are at higher risk to deliver low-birth weight babies. Maternal stressful events prior to conception also have a negative impact on birth weight and can result in a higher risk for preterm and lower birth weight babies. Women who experienced abuse (physical, sexual, or emotional) during pregnancy are also at increased risk of delivering a low-birth weight baby. The theory is that stress can impact a baby based on two different mechanisms: neuroendocrine pathway or immune/inflammatory pathway. Stress causes the body to produce stress hormones called glucocorticoids that can suppress the immune system., as well as raises levels of placental corticotropin-releasing hormone (CRH) which can lead to preterm labor. One way to decrease rates of low birth weight and premature delivery is to focus on the health of women prior to conception through reproductive education, screening and counseling regarding mental health issues and stress, and access to primary care (Cheng, Kotelchuck & Guyer, 2012).
Environmental factors, including exposure of the mother to secondhand smoke can be a factor in determining the birth weight of child. Children born to mothers who smoked or were exposed to secondhand smoke are more likely to develop health problems earlier in life such as neurodevelopmental delays. When mothers actively smoke during pregnancy, their child is at a higher risk of being born with a low birth weight. Smoking can also be a stress management tool used by expecting mothers (Mahumud, Sultana & Sarker, 2017).
The health of the mother during the pregnancy can affect birth weight. A pre-existing disease or acquired disease in pregnancy is sometimes associated with decreased birth weight. For example, celiac disease confers an odds ratio of low birth weight of approximately 1.8. Certain medications (e.g. for high blood pressure or epilepsy) can put a mother at a higher risk for delivering a low birth weight baby. Women younger than 15 or older than 35 are at a higher risk to have a low-birth weight baby. Multiple births, where a mother has more than one child at one time, can also be a determinant in birth weight as each baby is likely to be outside the AGA (appropriate for gestational age). Multiple births put children at a higher rate to have low birth weight (56.6%) compared to children born in a single birth ( 6.2%). Low birth weight can also vary by maternal age (Tersigni, Castellani, de Waure, Fattorossi, De Spirito, Gasbarrini, et al., 2014).
The following according to Fink (2020) are some of the some of the health factors that affect the weight of newborns:
- High Blood Pressure: Most pregnant women with high blood pressure give birth to completely healthy babies. But high blood pressure in a mom-to-be can cause low birth weight in her baby. That’s because high blood pressure in the mom can interfere with the delivery of oxygen and nutrients to her baby. High blood pressure can also cause premature birth, and babies who are born early are typically smaller than babies born at term. Both chronic high blood pressure (high blood pressure that existed prior to the pregnancy) and gestational hypertension (high blood pressure that develops during pregnancy) have been associated with low birth weight. If you have a history of high blood pressure, work with your doctor to keep it under control during your pregnancy (Fink, 2020).
- Diabetes: If a mom-to-be has diabetes–either pre-existing diabetes or gestational diabetes—she’s more likely to deliver a high birth weight baby, particularly if her blood sugars are not well controlled during the pregnancy. That’s because the extra sugar in mom’s bloodstream passes through the placenta to her baby. The baby essentially receives more nutrition than he needs and grows larger than normal. It’s a different story if dad has diabetes. If a child’s father has diabetes, the baby faces an increased risk of low birth weight (Fink, 2020).
- Heart Disease: Women with heart disease are more likely to give birth to low birth weight babies. That’s because heart disease interferes with the heart’s ability to pump oxygen- and nutrient-carrying blood to the baby, via the placenta. A mother’s likelihood of delivering a low birth weight baby seems linked to the severity of her heart disease—the more severe the heart disease, the greater the chance of low birth weight (Fink, 2020).
- Asthma: Poorly controlled or severe asthma in mothers-to-be has been associated with low birth weight babies. Research has shown women who have daily symptoms or poor air flow are more likely to have low birth weight babies than women with well-controlled asthma (Fink, 2020).
- Kidney Disease: Kidney disease in the mother can affect an infant’s weight. If the mom has mild kidney disease and no other health problems, the baby is likely to be healthy. Moderate and severe kidney disease increases the risk of premature birth and a low birth weight baby (Fink, 2020).
- Lupus: Lupus, a chronic autoimmune disease that’s most prevalent in women of childbearing age, increases the risk of intrauterine growth retardation (IUGR) and low birth weight. That risk seems to be increased if the mother-to-be is taking steroid medication or has high blood pressure. Women should work with their healthcare providers to devise a treatment plan that balances their needs with their babies’ needs. A pregnant woman with lupus will likely undergo many ultrasounds during her pregnancy to monitor the baby’s growth. Stress tests are also used to check the baby’s health (Fink, 2020).
- Anemia: Anemia, or a low red blood cell count, in the mother increases the risk of a low birth weight baby. That’s likely because the red blood cells are responsible for carrying oxygen and nutrients throughout the body. The most common type of anemia is iron-deficiency anemia, and it’s easily prevented or treated with iron supplements. That’s why prenatal vitamins typically include iron. Making sure moms-to-be get enough iron is one way to make sure babies are born at a healthy weight (Fink, 2020).
- Dental Health: The mouth might be far from the womb, but there’s evidence to suggest gum disease in the mother increases the risk of preterm birth and low birth weight. No one is quite sure why or how gum disease is linked to poor pregnancy outcomes, but moms-to-be now have another reason to brush, floss and visit the dentist. Prenatal visits during pregnancy give your healthcare provider a chance to monitor your baby’s growth and your overall health and to tweak your treatment plan, if necessary. Keeping your health under control is the best thing you and your partner can do for your baby (Fink, 2020).
Impacts of Birth Weight on Health
The impact of birth weight on health can be classified into two influence of birth weight on the first few year of life and the influence of birth weight on adult life.
Influence of Birth Weight on the First Few Years of Life
Children born with an abnormally low birth weight can have significant problems within the first few years of life. They may have trouble gaining weight, obtaining adequate nutrition, and supporting a strong immune system. They also have higher risks for mortality, behavior problems, and mental deficiencies. Low birth weight babies are more likely to develop breathing problems (infant respiratory distress syndrome), bleeding in the brain (intraventricular hemorrhage), patent ductus arteriosus (PDA), necrotizing enterocolitis, retinopathy of prematurity, jaundice and infections. That said, the effects of low birth weight on a child’s first few years of life are often intertwined with other maternal, environmental, and genetic factors and most effects of low birth weight are only slightly negatively significant on a child’s life when these factors are controlled for. When these factors are controlled, the only significant effect low birth weight has on a child’s development is physical growth in the early years and the likelihood of being underweight compared to normal birth weight babies (Datar & Jacknowitz, 2009).
Influence of Birth Weight on Adult Life
Studies have been conducted to investigate how a person’s birth weight can influence aspects of their future life. This includes theorised links with obesity, diabetes and intelligence. A baby born small or large for gestational age (either of the two extremes) is thought to have an increased risk of obesity in later life, but it was also shown that this relationship is fully explained by maternal weight. Middle aged adults with low birth weight present with a higher chance of obesity and diabetes. Babies that have a low birth weight are thought to have an increased risk of developing type 2 diabetes in later life. Low birth weight is linked with increase rates of obesity, insulin resistance, and type 2 diabetes and it is shown that children with the low birth weights have increased leptin levels after they catch up growth during childhood. Adiponectin levels are positively related with birth weight and BMI in babies with an increase of risk of type 2 diabetes. The leptin and adiponection mechanisms are still being studied when involving low birth weight (Jornayvaz, Vollenweider, Bochud, Mooser, Waeber & Marques-Vidal, 2016).
Measures to Prevent Common Birth Defects
According to Centre for Disease Control and Prevention (CDC) (2020), not all birth defects can be prevented, but women can increase their chances of having a healthy baby by managing health conditions and adopting healthy behaviors before becoming pregnant. This can be achieved by making a commitment to yourself, to get healthy before and during pregnancy by actively trying to plan ahead, avoid harmful substances, choose a healthy lifestyle, and talk with your healthcare provider.
The following are some of the measures as recommended by the CDC (2020):
- Get 400 Micrograms (mcg) of Folic Acid Everyday: Folic acid is a B vitamin. If a woman has enough folic acid in her body at least one month before and during pregnancy, it can help prevent major birth defects of the developing brain and spine (anencephaly and spina bifida). Women can get folic acid from fortified foods or supplements, or a combination of the two, in addition to a varied diet rich in folate (CDC, 2020).
- See a Healthcare Professional Regularly: A woman should be sure to see her doctor when planning a pregnancy and start prenatal care as soon as she thinks that she is pregnant. It is important to see the doctor regularly throughout pregnancy, so a woman should keep all her prenatal care appointments (CDC, 2020).
- Avoid Alcohol at Any Time During Pregnancy: Alcohol in a woman’s bloodstream passes to the developing baby through the umbilical cord. There is no known safe amount of alcohol use during pregnancy or while trying to get pregnant. There is also no safe time during pregnancy to drink. All types of alcohol are equally harmful, including wine and beer. Drinking alcohol during pregnancy can cause miscarriage, stillbirth, and a range of lifelong physical, behavioral, and intellectual disabilities. These disabilities in the child, which occur because the mother drank alcohol during the pregnancy, are known as fetal alcohol spectrum disorders (FASDs) (CDC, 2020).
- Avoid Smoking Cigarettes: The dangers of smoking during pregnancy include preterm birth, certain birth defects (cleft lip or cleft palate), and infant death. Even being around tobacco smoke puts a woman and her pregnancy at risk for problems. Quitting smoking before getting pregnant is best. For a woman who is already pregnant, quitting as early as possible can still help protect against some health problems for the baby, such as low birth weight (CDC, 2020).
- Avoid Marijuana and Other Drugs: A woman who uses marijuana or other drugs during pregnancy can have a baby who is born preterm, of low birth weight, or has other health problems, such as birth defects. Marijuana is the illicit drug most commonly used during pregnancy. Since we know of no safe level of marijuana use during pregnancy, women who are pregnant, or considering becoming pregnant, should not use marijuana, even in states where marijuana is legal. Women using marijuana for medical reasons should speak with their doctor about an alternative therapy with pregnancy-specific safety data (CDC, 2020).
- Prevent Infections: Some infections that a woman can get during pregnancy can be harmful to the developing baby and can even cause birth defects (CDC, 2020).
- Avoid Overheating and Treat Fever Promptly: During pregnancy, a woman should avoid overheating and treat fever promptly. Overheating can increase a woman’s chance of having a baby with a neural tube defect. It can be caused by a fever or exposure to excessive temperatures (like getting in a hot tub) that increases a woman’s core temperature. Protecting against infections, treating fever promptly, limiting environmental exposures known to increase core body temperatures (like getting in a hot tub), and consuming 400 micrograms (mcg) of folic acid every day can help reduce the chance of having a baby born with a neural tube defect (Kerr, Parker, Mitchell, Tinker & Werler, 2017).
- Keep Diabetes Under Control: Poor control of diabetes during pregnancy increases the chances for birth defects and other problems for the pregnancy. It can also cause serious complications for the woman. Proper healthcare before and during pregnancy can help prevent birth defects and other poor outcomes (CDC, 2020).
- Strive to Reach and Maintain a Healthy Weight: A woman who is obese (a body mass index [BMI] of 30 or higher) before pregnancy is at a higher risk for complications during pregnancy. Obesity also increases a pregnant woman’s risk of several serious birth defects. Even if a woman is not actively planning a pregnancy, getting healthy can help boost her health and her mood. If a woman is overweight or obese, she should talk with her doctor about ways to reach a healthy weight before she gets pregnant (CDC, 2020).
- Talk to a Healthcare Provider about taking any Medications: We know that certain medications can cause serious birth defects if they are taken during pregnancy. For many medications taken by pregnant women, the safety has been difficult to determine. Despite the limited safety data, some medications are needed to treat serious conditions. If a woman is pregnant or planning a pregnancy, she should not stop taking medications she needs or begin taking new medications without first talking with her healthcare provider. This includes prescription and over-the-counter medications and dietary or herbal products (CDC, 2020).
- Talk to a Healthcare Provider about Vaccinations (Shots): Most vaccinations are safe during pregnancy and some vaccinations, such as the flu vaccine and the Tdap vaccine (adult tetanus, diphtheria and acellular pertussis vaccine), are specifically recommended during pregnancy. Some vaccines protect women against infections that can cause birth defects. Having the right vaccinations at the right time can help keep a woman and her baby healthy. She should talk to her doctor about which vaccines are recommended for her during pregnancy (CDC, 2020).
Centre for Disease Control and Prevention (2020). Commit to Healthy Choices to Help Prevent Birth Defects. Retrieved from https://www.cdc.gov/ncbddd/birthdefects/prevention.html on 10th May, 2021.
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Datar A. & Jacknowitz, A. (2009). “Birth weight effects on children’s mental, motor, and physical development: evidence from twins data”. Maternal and Child Health Journal. 13 (6): 780–94. doi:10.1007/s10995-009-0461-6.
Fink, J. L.W. (2020). 8 Health Factors That Affect a Baby’s Birth Weight. Retrieved from https://www.healthgrades.com/right-care/pregnancy/8-health-factors-that-affect-a-babys-birth-weight on 7th May, 2021
Jornayvaz, F.R., Vollenweider, P., Bochud, M., Mooser, V., Waeber, G. & Marques-Vidal, P. (2016). “Low birth weight leads to obesity, diabetes and increased leptin levels in adults: the CoLaus study”. Cardiovascular Diabetology. 15: 73. doi:10.1186/s12933-016-0389-2.
Kerr, S.M., Parker, S.E., Mitchell, A.A., Tinker, S.C. & Werler, M.M. (2017). Periconceptional maternal fever, folic acid intake, and the risk for neural tube defects. Annals of epidemiology. 27(12):777-782.e771.
Mahumud, R.A., Sultana, M. & Sarker, A.R. (2017). “Distribution and Determinants of Low Birth Weight in Developing Countries”. Journal of Preventive Medicine and Public Health = Yebang Uihakhoe Chi. 50 (1): 18–28. Doi:10.3961/jpmph.16.087.
MedlinePlus, 2020). Birth Weight. Retrieved from https://medlineplus.gov/birthweight.html on 7th May, 2021.
Tersigni, C., Castellani, R., de Waure, C., Fattorossi, A., De Spirito, M., Gasbarrini, A., et al. (2014). “Celiac disease and reproductive disorders: meta-analysis of epidemiologic associations and potential pathogenic mechanisms”. Human Reproduction Update. 20(4): 582–93. doi:10.1093/humupd/dmu007.
Yaghootkar, H. & Freathy, R.M. (2012). “Genetic origins of low birth weight”. Current Opinion in Clinical Nutrition and Metabolic Care. 15 (3): 258–64. doi:10.1097/mco.0b013e328351f543.