The answer is NO, and I am actually quite surprised by this conclusion! I thought that the upward trend in adult weight gain, type 2 diabetes, and processed food consumption in this country would be accompanied by an average increase in fetal weight. However, research from Harvard Pilgrim Health Care Institute’s Department of Population Medicine (an affiliate of Harvard Medical School) states in a study from the February 2010 issue of Obstetrics & Gynecology that birth weights have actually decreased an average of 52 grams (1.83 ounces) leaving the average birth weight of a newborn at 7 lbs 7 ounces.
This study analyzed data collected during the past 15 years and included 36,827,828 American babies born at full-term. Keep in mind that full term is considered to be anything past 37 weeks. In addition to the decrease in birth weight, the study also found that babies are being born an average of 2.4 days earlier than term (ie the “estimated due date” of 40 weeks). This is relevant because babies born earlier tend to weigh less, since they had less time to grow.
There is still speculation among researches and doctors as to why this decline has occurred. “We were startled by the findings,” said Dr. Emily Oken, author of the study and assistant professor of population medicine at Harvard Medical School “We tried really hard to explain it away but we were unable to. Dr. Peter Bernstein, director of the Maternal Fetal Medicine Fellowship Program at Montefiore Medical Center in New York City commented that this was NOT the trend he was seeing amongst his clients. However, Bernstein admitted that his experience is confined to the Bronx, where there is a high incidence of obesity and diabetes. “If you look at different populations, you get different results,”. Speaking from my own limited personal experience as a labor support doula, over 7 years and 80 births I have mostly seen babies weighing in the high 7- to 8-pound range.
Bigger babies tend to correlate with older mothers and nonsmokers. So with a national increase in maternal age and a decrease in tobacco use, one would expect fetal birth weight to have increased amongst this population. In fact, the study showed that low-risk women (defined, in this case, as educated, married, white, nonsmokers, with early prenatal care and uncomplicated vaginal deliveries) were having babies weighing on average, 2.79 ounces less in 2005 than 1999.
Oken shared another thought, “Over the second half of the 20th century, birth weight increased, so it is possible that this [recent decline] represents a plateauing of that increase in birth weights that was observed over the last 50 or 70 years, and we are getting back to a steadier state.” If fetal weight correlates with maternal weight gain, however, it seems very odd that we are plateauing only now; in generations past, doctors and care providers were much more stringent on how much maternal weight was gained during pregnancy. In the 1960s, for example, women were encouraged to limit their weight gain to a maximum of 22 pounds. Currently, the average maternal weight gain is 33 pounds.
Perhaps the connection between maternal weight gain and fetal weight is not so clear after all. Several studies have compared maternal weight gain to the outcome of fetal weight, but these studies have produced conflicting information. One study states “The results confirmed that excessive maternal weight gain in pregnancy (> 35 lbs), does result in higher birth weight infants.” While another one states “excessive weight gain during pregnancy results in an increase in maternal weight, but not necessarily in increased birthweight.”
For the past 20 years, many care providers have adopted the guidelines of the Institute of Medicine (IOM) which advises proper maternal weight gain based on pre-pregnancy Body Mass Index (BMI). Just recently, the IOM has revised their guidelines, putting a cap on weight gain for obese women. These guidelines offer a range of healthy weight gain based on expectant mother being underweight, normal, overweight or obese pre-conception. When determining where one fits into these 4 categories, factors are not measured purely by pounds, but by a ratio of height and weight.
Shifting the focus from weight gain to maintaining a safe BMI seems like a move in the right direction. It’s very clear to me that healthy weight gain during pregnancy is not a “one size fits all” issue. There are definite risks associated with both too little maternal weight gain and too much. Taking into consideration the sensitivity many women have with respect to weight gain and body image, it may be helpful consult with your care provider on the individual guidelines and nutritional support that might be best for you. So while the researchers sort out the data on this connection between maternal weight gain and fetal weight, the best advice seems to be paying more attention to a healthy diet and proper exercise than the number on the scale.
For more on estimated fetal birth weight and the risks involved with a larger baby, take a look at this blog entry.
For more on maternal weight gain, please click here.
February 23rd, 2010
My last two doula clients were both induced due to a diagnosis of Oligohydramnios - low amniotic fluid. I have heard many of my students report that they were induced for the same reason, or that it was a very big concern for their care provider. I decided it was time to really understand the ins and outs of this condition.
What is amniotic fluid?
By the 12th day after conception, the amniotic sac will start to form. Within this protective barrier lives the baby, the placenta, the umbilical cord and the baby’s amniotic fluid. The amniotic fluid is a clear, slightly yellowish, odorless substance. At the onset of pregnancy, as the amniotic fluid starts to build in the amniotic sac, it comes from the mother. Over time, the fetus adds to the supply of amniotic fluid through a shedding of skin cells, along with floating stem cells and the baby’s own urine. As the baby breathes in and ingests the fluids, it urinates them out, and this is the basic cycle that continues until the baby is born.
What is the importance of the amniotic fluid?
The amniotic fluid has many roles. For one, it acts as a buffer or cushion should the mother slip or experience jerky, jarring movements. The baby is basically floating around in this big sac of fluid, so should the mother stumble, the baby will not likely feel the impact. This “floating” idea also helps protect the baby from compressing its umbilical cord, which would deprive the baby of oxygen and put the baby in distress. This pool of fluid also gives the baby room to move, which helps the baby build muscle tone and a strong skeleton, protecting it against infection.
Amniotic fluid is also important with regard to the healthy development of the lungs and gastrointestinal system. When there’s little fluid (in the case of a congenital abnormality of the bladder or missing kidneys, for example) the trachea and other respiratory structures don’t mature, indicating that the pressure and nature of the fluid is important in these organs’ growth. Because the lungs are one of the last systems to emerge in fetal development, fluid levels may be a greater concern earlier in pregnancy, especially when there is a premature rupture of the membranes.
What are the concerns with “low fluids”?
Low fluids can be of concern because there will be a higher likelihood of cord compression during labor. As discussed above, the fluid helps keep the baby buoyant.
Low fluids can be an indication of other problems, such as:
*Kidney or urinary tract issues for the baby
*Pre-eclampsia, diabetes, or high blood pressure for the mother
*Partial abruption of the placenta
*PROM - Premature Rupture of the Membranes
*Intrauterine Growth Restriction (IUGR)
How is it measured?
Amniotic fluid is measured with an ultrasound. The technician measures the fluids in 4 quadrants of the uterus and adds the measurements together to see how many centimeters of fluid are in the uterus. The AFI or Amniotic Fluid Index rates the fluids, with 5 cm being too little fluid and 25 cm being too much.
What can be done if this condition is suspected?
In the US, oligohydramnios is a complication in 0.5-5.5% of all pregnancies, and severe oligohydramnios (meaning less then 400 ml of fluids) is a complication in 0.7% of pregnancies. Oligohydramnios is more common in pregnancies beyond term because the AFV (Amniotic Fluid Volume) normally decreases at term. It complicates as many as 12% of pregnancies that last 41 weeks and longer. According to Anne Frye, in Holistic Midwifery “If abnormal quantities of fluid is suspected, assess the situation over the course of several prenatal visits; fetal growth spurts and lags as well as fluid volume are not always consistent from week to week in normal pregnancy” The “wait, see and re-asses” approach may be helpful in determining what kind of reaction is necessary.
Also, since dehydration may be a cause for the low fluid levels, you might ask your care practitioner if you can hydrate and return the next day to be retested.
Another option is an amnio-infusion, which reintroduces fluids into the amniotic sac. During labor, the doctor can pass a catheter through the cervix and add a warm saline solution. This is helpful if the concern is cord compression.
A similar approach can be used if the mother is not already in labor and it is too early to induce her. The doctor can perform an amniocentesis to reintroduce fluid into the amniotic sac. Although oligohydramnios often returns soon after this procedure, it can help your doctor visualize the fetal anatomy and accurately determine fetal development.
The final solution for oligohydramnios is to induce labor.
Final food for thought: a study from The Johns Hopkins Hospital which discusses the outcome of births with suspected low fluids.
Low Levels of Amniotic Fluid No Risk To Normal Birth
Doctors may not have to deliver a baby early if it has low levels of amniotic fluid surrounding it, Johns Hopkins obstetricians report.
In a study to be presented Feb. 7 [2003] at the annual meeting of the Society for Maternal-Fetal Medicine in San Francisco, researchers show that babies born under such conditions fared similarly to those born to women whose wombs held normal amounts of amniotic fluid. No significant differences were found in the babies’ birth weights, levels of acid in the umbilical cord blood, or lengths of stay in the hospital.
Typically, doctors have been concerned about women with low levels of amniotic fluid during the third trimester – a condition called oligohydramnios – because too little fluid can be associated with incomplete development of the lungs, poor fetal growth and complications with delivery. Amniotic fluid is measured by depth in centimeters. Normal amounts range from 5 to 25 centimeters; any amount less than 5 centimeters is considered low.
“These study results are very surprising – they go against the conventional wisdom,” says Ernest M. Graham, M.D., senior author of the study and assistant professor of gynecology and obstetrics. “Amniotic fluid stems from the baby’s urine, and the urine results from good blood flow, so if we see low fluid we assume there probably is not good blood flow and the fetus is compromised. This study shows the fluid test is not as good as we thought, and there is most likely no reason to deliver the baby early if other tests are normal.”
The researchers studied 262 women (131 with oligohydramnios and 131 with normal amounts of amniotic fluid) who gave birth at The Johns Hopkins Hospital between November 1999 and July 2002, comparing the babies’ health at birth. Patients with oligohydramnios were delivered sooner, but were less likely to need Cesarean sections. Babies born to moms with isolated low amniotic fluid were normal size and were at no increased risk of respiratory problems, immature intestines or brain disorders.
Study co-authors were Rita Driggers, Karin Blakemore and Cynthia Holcroft.
Abstract # 318: Driggers, R. et al, “Are Neonatal Outcomes Worse in Deliveries Prompted by Oligohydramnios?”
February 11th, 2010
