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The third trimester of pregnancy begins in week 28 and continues until birth. During this time, the fetus grows larger and matures. It also moves a great deal between week 27 and 32 when its organs are sufficiently developed and it is still small enough to shift positions comfortably inside its mother's uterus. In the last two months, Baby becomes too big to move around, and by the end of the last trimester, just before birth, it usually settles into the uterus head down and gets ready to come out. Although the official due date in a pregnancy is the end of week 40, a full-term pregnancy can deliver anytime between the 37th and 42nd weeks of pregnancy.
Babies born before full term (anytime before week 37) are known as premature, because their organs, particularly their lungs, are not developed enough to survive in a natural environment. "Premies" must be kept in hospital conditions that are as similar to the womb as possible until their lungs are strong enough to breathe air. Due to advances in modern medicine, particularly the technology of intensive care, premature babies have steadily increased their chances of survival to the point where the outer boundary of viability is now about 28 weeks. In other words, babies born anytime during the third trimester have a good chance of survival. Nonetheless, premature birth continues to be a serious threat, because even if the baby survives outside the womb, it may have fragile organs that cause poor health in later life. For this reason, doctors do everything they can to help babies stay inside their mother's wombs until week 37.
Even if the longest possible pregnancy is the best option for Baby, it is not always easy for Mom. Expecting mothers gain the most weight in the last trimester, largely because the fetus enters its most rapid stage of growth and gains up to 28g per day. In the last few weeks their bellies flop around and drop very low as Baby moves its head downward into the pelvic cavity, the ideal position for birth.
The most common symptoms during third trimester include fatigue, constipation, hemorrhoids, heartburn, swollen feet and ankles, frequent urination, insomnia and discomfort during sleep, hand pain and numbness, shortness of breath because the uterus is pressed up against the lungs, aches and pains in the back, the pelvis and the hip, and Braxton Hicks contractions, which do not lead to labor, but exercise the uterus without opening the cervix.
In the last trimester, an expecting mother often feels constantly fatigued by the combination of sleeplessness and the weight of a large fetus inside the body. She may also develop hemorrhoids -- swollen veins in the intestine and the anus -- because of the pressure her enlarged uterus puts pressure on her inferior vena cava, the vein that drains the large intestine. Another common problem is constipation, infrequent and difficult bowel movements, caused both by a slow-moving digestive system and possibly by the iron supplements a doctor has prescribed to ensure the good health of the baby.
As the due date approaches, and it is almost time to go into labor, the fetus will settle into mother's pelvis in what is called lightening or dropping. The cervix begins to thin out (effacement) and open up (dilation). Braxton Hicks contractions become stronger, more frequent, and sometimes more painful. There is cramping in the lower back, the rectum and the groin.
The mother's water breaks about the same time that labor starts, perhaps just before or after. The membranes of the cervix rip open and water spills out from the mother's body. This means that it's time to go to the hospital, because baby is coming.
Once the mother's water has broken, labor progresses through three stages with increasing speed, and each stage is more painful than the one before. The process begins with increasingly frequent contractions, many minutes apart at first, and then only 3 or 4 minutes apart. In response to the contractions, the cervix gradually thins and opens, wider and wider until it is fully dilated and there is an open space at least 10 centimeters wide where the baby's head can come out. Contractions are gentle, short, and infrequent at first, during the "latent" or early phase of labor, but become long, strong and frequent during active labor.
Once the expecting mother is fully dilated, the second stage of labor begins and the mother begins to push, using all of her muscles to propel baby's body out of the uterus, through the cervix, and into the open air. This is the moment of birth. The third and final stage begins right after birth. While the baby begins getting used to life outside the womb, sometimes lying on mother and breastfeeding, or getting its vital signs checked by the doctor, other members of the birthing team remove the placenta from Mother's body and cut the umbilical cord that connects baby to the placenta.
The average length of labor for first time mothers at full term is between 10 and 20 hours, but it can last much longer for some women. For others, particularly those who've given birth before, it may be over in less than an hour. Just as some births are premature, others may be a few days late. Labor does not always begin on its own, even when the baby is ready for the outside world. In these cases, practitioners use medication and other techniques to induce contractions, or in the case of labor that starts but stalls, they can also speed up labor. Data from the U.S. Centers for Disease Control suggest that more than one in five births in the United States are induced. In situations where labor has not begun and induction would not be safe, practitioners go on to perform C-sections. *This article is based on the information at http://www.webmd.com,http://www.pregnancy.com,http://pregnancy.about.com and http://en.wikipedia.org |
