Even when a baby comes bellowing into the world at a hearty eight pounds, parents worry about its vulnerability. This worry is compounded for parents of preemies -- tiny babies weighing 5 pounds, 8 ounces, or less, typically born before 37 weeks.
About one in 12 U.S. infants are born with low birth weight, which carries the risk of infection, developmental delays, and even death, according to the March of Dimes. In fact, the number of babies born during the late preterm period of 34 to 36 weeks has risen 20 percent since 1990, according to the U.S. Centers for Disease Control and Prevention.
Here we walk you through the various causes of low birth weight in hopes that a greater understanding of the problem can help in its prevention, starting with No. 1 low birth rate risk: multiple pregnancy.
When a woman carries more than one baby, her risk of premature delivery skyrockets. Each additional baby increases the risk significantly: The preterm rates are approximately 60 percent for twins, 90 percent for triplets, and about 100 percent for quadruplets and beyond.
Why the dramatic risk increase? Additional babies stretch the uterus and compete for limited nutrients. Multiple pregnancies also put extra strain on the mother's body, sometimes leading to complications like anemia, high blood pressure, and early labor, according to the American Congress of Obstetricians and Gynocologists (ACOG).
And if you think you've seen a rise in multiple births in the United States, you'd be right. Women are getting pregnant later in life and moms in their 30s and 40s are most likely to conceive more than one baby. Adding to the odds of giving birth to multiples? Fertility treatments.
Did You Know?
To help stem the tide of multiple births, the American Society of Reproductive Medicine recently issued guidelines limiting the number of embryos that can implanted during in vitro fertilization.
Maternal Diseases and Infections
Women who have chronic conditions like diabetes, heart defects, or kidney disease tend to have more difficult pregnancies. As a result, they're more likely to deliver preterm and have low birth weight babies.
The American Congress of Obstetricians and Gynecologists (ACOG) advises these women to work closely with their physicians on managing their chronic conditions. Adjustments to diet, medications, and activity levels can help avert preterm delivery risk.
Pregnancy-specific complications and diseases can also lead to preterm birth. For example, if bacteria infect the uterus, immediate delivery is necessary.
Another threat is preeclampsia, with its hallmarks of high blood pressure and protein in the urine. This dangerous, little-understood disease most commonly affects older moms, first-time moms and moms of multiples. The disease cuts off nutrients to infants and can cause deadly seizures in mothers. Immediate delivery is the only sure way to save both mom and baby.
Other than high blood pressure and protein the urine, symptoms of preeclampsia may include swelling the hands, face or feet, headache, blurred vision and abdominal pain, according to the National Institutes of Health.
Did You Know?
Preeclampsia and it's more full-blown form, eclampsia, affect 10 percent of pregnancies in the United States, costing $3 billion a year and causing 15 percent of premature births, according to Preeclampsia.org. Medical researchers still don't know what causes the disease.
It might not come as a surprise that a baby's health may be impacted if the mother smokes during pregnancy. But did you know that it doubles the risk of delivering a low birth weight baby and increases the risk of delivery of a preterm birth?
The main reason is that smoking delivers the harmful chemicals tar, nicotine, and carbon monoxide to the fetus. These substances reduce the baby's oxygen supply, slowing its growth and development. The more cigarettes a woman smokes, the more likely she is to have an underweight baby.
The good news: A mother can reduce her baby's risk of being born underweight by quitting smoking at any point in the pregnancy, according to the American Congress of Obstetricians and Gynecologists (ACOG).
Alcohol and Drugs
Over the past several decades, the public has grown increasingly aware of the problems drugs and alcohol can cause in pregnancy. Research has linked alcohol, illicit drugs -- and even some over-the-counter medications -- to birth defects and slowed development in infants.
The American Congress of Obstetricians and Gynecologists (ACOG) advises pregnant women to avoid all medications and drugs as much as possible, but to check with their doctor before discontinuing any prescription medications.
Some of the biggest developmental offenders are marijuana, heroin, cocaine, Ecstasy and other amphetamines. Heavy use of these drugs is associated with low birth weight, preterm birth, congenital problems, and learning and developmental disabilities.
Alcohol is perhaps the most commonly abused substance in pregnancy. In moderate to large amounts it can cause fetal alcohol syndrome -- a condition that may involve reduced baby size or weight as well as learning and developmental problems -- and raise the risk of premature delivery.
Problems with the Uterus or Cervix
The cervix, or opening to the uterus, serves as something of a lockbox in a pregnancy. When the fetus anchors itself in the womb, the cervix slams shut to secure the developing baby and keep out germs. But sometimes, in cases of cervical incompetence, the cervix fails to close properly. As the baby grows, it puts increasing pressure on the opening, possibly spurring premature labor and delivery.
Doctors typically manage cervical incompetence by putting a stitch in the cervix, known as a cerclage, to help keep the baby going through 37 to 38 weeks. In many cases, bed-rest is also advised.
Uterine fibroids and malformations of the uterus can also limit a baby's development. For example, a bicornuate uterus has two hornlike chambers instead of the usual oval shape. If the baby establishes in one of these smaller chambers, it has limited room to grow. In these cases, miscarriage or preterm delivery is often common, according to The American Academy of Family Physians (AAFP).
Did You Know?
Management of preterm labor and preterm birth account for health care expenditures of over $3 billion per year, according to the AAFP (Familydoctor.org).
The placenta is a nutrient-rich lifeline from mother to infant, so when it is compromised, the infant's growth can suffer.
Several types of placental problems can interfere with a baby's growth. One is placenta previa, in which the placenta fuses to the cervix, covering all or part of the opening. Even more common is placental abruption, in which the placenta starts separating from the uterine wall during the pregnancy, before delivery. Affecting about one percent of pregnancies, the condition can, in serious cases, reduce the flow of nutrients and oxygen to the baby.
Placental problems are often associated with preterm births and low birth weight.
To properly develop and thrive, infants need a steady, rich supply of nutrients from the mother. For example, folic acid helps establish the brain and spinal column, and proteins build the infant's exploding cells.
A healthy, varied diet -- high in fruits, vegetables, grains, nuts, lean meats and dairy -- is key to the development of a full-term, vigorous baby. On the other end of the spectrum, a diet restricted to foods low in nutritional value, like processed sweets, can slow fetal growth.
Not eating enough food during pregnancy can also limit a baby's growth. Recommended weight gain for a typical pregnancy is 25 to 35 pounds, according to the American Congress of Obstetricians and Gynecologists (ACOG).
Did You Know?
Doctors recommend that women take 400 micrograms of folic acid daily for at least a month before becoming pregnant, and during the first three months of pregnancy to help prevent defects of the spine and skull.
As much as pregnant women may act like heroes, some even working at the office every day right up to delivery, this is a sensitive time for them and their babies.
During pregnancy, women's bodies are pumping 40 to 50 percent more blood than usual -- their hearts working 30 to 50 percent harder -- and they can feel tired and uncomfortable, according to the Cleveland Clinic's Center for Continuing Education.
But the fact is, many pregnant women work for a living, some of them putting in long work hours and standing for extended periods of time. That toiling can put extra stress on a pregnancy, possibly interfering with fetal growth and full-term delivery. Other contributors to pregnancy stress are exposure to harmful chemicals (in factories for example, or while cleaning the house) or lack of emotional support from family and friends.
Some birth defects can impede normal development in the infant and lead to preterm birth. For example, if an infant develops problems like transposition of the heart's great arteries or spina bifida (open spine) -- a condition in which the neural tube fails to close properly -- doctors may need to perform surgery while the baby is still in the womb, which raises the risk of preterm birth.
A recent study in the journal Obstetrics & Gynecology found that the birth defects most commonly associated with preterm delivery include:
- Down syndrome
- Klinefelter syndrome
- Turner syndrome
- Patau syndrome
- Edwards syndrome
- Congenital structural abnormalities, including orofacial cleft, club foot,
- polydactyly, hypospadias, and spina bifida
- Cardiac, central nervous system, musculoskeletal abnormalities
Did You Know?
Heart defects are the most common of all birth defects, affecting one in every 100 to 200 pregnancies. Defects of the palate and lip -- cleft lip and cleft palate -- are next, followed by defects of the spine and brain and Down syndrome, according to the U.S. Centers for Disease Control and Prevention (CDC).
For a pregnant mom, catching a common illness like a cold or the flu can raise concerns about harm to the baby. But these everyday illnesses don't typically threaten a developing infant.
There are, however, some less common viral and parasitic infections that can indeed cause fetal problems like slow growth, and even birth defects. According to the U.S. Centers for Disease Control and Prevention (CDC), here are a few to watch for:
- Cytomegalovirus. This herpes virus present in bodily fluids is the most common type of virus transmitted to a developing infant. It is associated with disabilities like neural tube defects and Down syndrome.
- Rubella. More commonly known as German measles, this virus can cause birth defects like mental retardation and hearing, sight, and heart problems. Luckily, German measles can be prevented via the Measles, Mumps, and Rubella (MMR) vaccine.
- Chickenpox. Exposure to this virus during the first or second trimester is associated with a small chance of congenital varicella syndrome, which can include limb malformation, scarring, growth problems, and mental disabilities.
- Toxoplasmosis. Infection with this parasite during pregnancy is associated with brain defects and hearing and sight loss. The parasite can be present in undercooked meat and cat feces.
Premature delivery can be a scary thing. Read one mother's story of premature delivery to learn about the process and emotions of delivering a preemie.