Fetal Lungs Provide a Signal Initiating Labor

This isn't new information (the press release below was published in 2004), but it seems to be relatively unheard of among mothers and childbirth educators. It has significant implications and should greatly influence families' decisions about inducing labor or electing to deliver a baby via cesarean section. If the mother has not gone into labor, the baby most likely has not given the signal that he's ready!

A protein released from the lungs of a developing mouse fetus initiates a cascade of chemical events leading to the mother's initiation of labor, researchers at UT Southwestern Medical Center at Dallas have found.

The research, which has implications for humans, marks the first time a link between a specific fetal lung protein and labor has been identified, said Dr. Carole Mendelson, professor of biochemistry and obstetrics and gynecology and senior author of the study. The paper appears in an upcoming issue of the Proceedings of the National Academy of Sciences and is currently available online.

The initiation of term labor is carefully timed to begin only after the embryo is sufficiently mature to survive outside the womb. Previous studies suggested that the signal for labor in humans may arise from the fetus, but the nature of the signal and actual mechanism was unclear, Dr. Mendelson said.

In their study, UT Southwestern researchers found evidence that a substance secreted by the lungs of a developing fetus contains the key signal that initiates labor. The substance, called surfactant, is essential for normal breathing outside the womb.

"We found that a protein within lung surfactant serves as a hormone of labor that signals to the mother's uterus when the fetal lungs are sufficiently mature to withstand the critical transition to air breathing," Dr. Mendelson said.

"No one really understands what causes normal or preterm labor. There may be several chemical pathways that lead to labor, but we think that this surfactant protein, which is also produced by the fetal lung in humans, may be the first hormonal signal for labor," said Dr. Mendelson, who is co-director of the North Texas March of Dimes Birth Defects Center at UT Southwestern.

In humans the signaling protein, called surfactant protein A, or SP-A, also helps immune cells, called macrophages, fight off infections in the lungs of children and adults by gobbling up bacteria, viruses and fungi that infiltrate the lung airway.

"Women who go into preterm labor frequently have an infection of the membranes that surround the fetus, and the number of macrophages in the wall of the uterus increases with the initiation of preterm labor. When women go into labor at term, they also have an increase in macrophages in the uterus," Dr. Mendelson said.

This led the researchers to investigate whether there was a connection between what happens during normal labor at term and in infected mothers who go into early labor.

"This also raised the question: If bacterial infection can cause increased macrophage infiltration of the uterus in preterm labor, what is the signal for the enhanced macrophage migration to the uterus at term?" Dr. Mendelson said.

In mice, the developing fetal lung starts producing SP-A at 17 days gestation; full-term delivery occurs at 19 days. The developing human fetus starts producing SP-A in increasing amounts after 30 to 32 weeks of a 40-week normal gestation, at which time the baby's lungs are essentially developed. As the fetus "breathes" amniotic fluid in the womb, the protein is released into the fluid.

"The SP-A protein binds to macrophages in the amniotic fluid, macrophages that come from the fetus itself," said Dr. Jennifer Condon, a postdoctoral researcher in biochemistry and the study's lead author.

The macrophages, "activated" by the protein, make their way through the amniotic fluid to the wall of the uterus. Once embedded there, they produce a chemical that stimulates an inflammatory response in the uterus, ultimately leading to labor.

http://www.utsouthwestern.edu/utsw/cda/dept37389/files/158762.html

Canadian Research Suggests Maternal IV Fluids Linked to Newborns' Weight Loss

BioMed press release.

A newborn baby's weight loss is often used to determine how well a baby is breastfeeding, and concern about a baby which loses too much weight may result in supplementing breastfeeding with formula. However, many women receive IV fluids during labor, and new research published in BMC's open access journal International Breastfeeding Journal shows that some of a newborn's initial weight loss may be due to the infant regulating its hydration and not related to a lack of breast milk.

A group of Canadian researchers looked at relationships among the IV fluids a mother received during labor (or prior to her caesarean section), neonatal output (measured by diaper weight), and newborn weight loss. They found that during the first 24 hours following birth there was a positive association both between the IV fluids given to mothers before birth and neonatal output, and between the neonatal output and newborn weight loss. At 60 hours post birth, the time of the average lowest weight, there was a positive relationship between maternal IV fluids and newborn weight loss.

"Nurses, midwives, lactation consultants, and doctors have long wondered why some babies lose substantially more weight than others even though all babies get small amounts to eat in the beginning," said principal investigator Prof Joy Noel-Weiss from the School of Nursing at the University of Ottawa's Faculty of Health Sciences. "It appears neonates exposed to increased fluids before birth might be born overhydrated, requiring the baby to regulate his or her fluid levels during the first 24 hours after birth."

Prof Noel-Weiss added, "We should reconsider the practice of using birth weight as the baseline when calculating newborn weight loss in the first few days following birth. For mothers and their breastfed babies, accurate assessment of weight loss is important. Although more research is needed, based on our findings, we would recommend using weight measured at 24 hours post birth as a baseline."

Alongside this article, the researchers have provided a standardized method for clinicians to collect and analyze data about newborn weight loss in their own maternity site, in the hope that this protocol will help them to make informed decisions when assessing newborn weight changes.

1. An observational study of associations among maternal fluids during parturition, neonatal output, and breastfed newborn weight loss. Joy Noel-Weiss, A Kirsten Woodend, Wendy E. Peterson, William Gibb and Dianne L Groll. International Breastfeeding Journal (in press)

2. Iatrogenic newborn weight loss: knowledge translation using a study protocol for your maternity setting . Joy Noel-Weiss, A Kirsten Woodend and Dianne L Groll. International Breastfeeding Journal (in press)