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Women go through many changes during each stage of pregnancy. Many of the pregnancy symptoms they have and the changes they deal with are common to all healthy pregnancies. The stages of embryonic and fetal development also follow a common pattern.
Still, pregnancy can be confusing and sometimes mysterious. It’s normal to wonder what happens during each of the stages of pregnancy.
Whether you are pregnant, are a concerned partner or friend, or are just curious, you may have many questions. Here is a description of the stages of pregnancy and the changes that women go through during a healthy pregnancy.
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Pregnancy is divided into 3 trimesters. Each trimester is a little longer than 13 weeks. The first month marks the beginning of the first trimester.
Gestational age can be confusing. Most people think of pregnancy as lasting nine months. And it’s true that a woman is pregnant for about nine months. But because pregnancy is measured from a woman’s last menstrual period — about 3-4 weeks before she is actually pregnant — a full-term pregnancy usually totals about 40 weeks from LMP — roughly 10 months.
Many women do not remember the exact date of their last menstrual period — that’s OK. The surest way to tell gestational age early in pregnancy is with ultrasound.
These are the first two weeks of a woman’s menstrual cycle. She has her period. About 2 weeks later, the egg that is most mature is released from the ovary — ovulation. Ovulation may happen earlier or later, depending on the length of a woman’s menstrual cycle. The average menstrual cycle is 28 days.
After it is released, the egg travels down a fallopian tube toward the uterus. If the egg meets a sperm, they combine to form one cell. This is called fertilization. Fertilization is most likely to occur when a woman has unprotected vaginal intercourse during the 6 days that lead into ovulation.
The fertilized egg moves down the fallopian tube and divides into more and more cells. It reaches the uterus about 3–4 days after fertilization. The dividing cells then form a ball that floats free in the uterus for about 2–3 days.
Pregnancy begins when the ball of cells attaches to the lining of the uterus. This is called implantation. It usually starts about 6 days after fertilization and takes about 3–4 days to be complete.
Pregnancy does not always occur. Up to half of all fertilized eggs pass out of women’s bodies during regular menstruation before implantation is complete.
Learn more about how pregnancy happens.
|A Woman’s First Signs of Pregnancy
For many women, the first sign of pregnancy is a missed period. Most pregnancy tests will be positive by the time a woman has missed her period. Other early signs of pregnancy include fatigue, feeling bloated, frequent urination, mood swings, nausea, and tender or swollen breasts. Not all women have all of these symptoms, but it is common to have at least one of them.
The ball of cells develops into an embryo at the start of the sixth week. The embryonic stage of pregnancy will last about 5 weeks. During this time all major internal organs begin developing.
The second month is often when pregnancy symptoms become very noticeable. Common discomforts like breast tenderness, fatigue, frequent urination, heartburn, nausea, and vomiting usually get worse. A woman’s body produces extra blood during pregnancy, and her heart beats faster and harder than usual to carry the extra blood.
The fetus is now measured from the top of its head to its buttocks. This is called crown-rump length (CRL).
Many of the pregnancy symptoms from the first 2 months continue — and sometimes worsen — during the third month. This is especially true of nausea. A woman’s breasts continue growing and changing. The area around the nipple — the areola — may grow larger and darker. Women who are prone to acne may experience outbreaks.
Women do not usually gain much weight during the first 3 months of pregnancy — usually about 2 pounds. Women who are overweight or underweight may experience a different rate of weight gain. Talk with your health care provider about maintaining a healthy weight throughout pregnancy.
Learn more about miscarriage.
The fourth month marks the beginning of the second trimester.
Some of the early signs and symptoms of pregnancy begin to be relieved during the fourth month. Nausea is usually reduced. But other digestive problems — heartburn and constipation — may be troublesome. Breast changes — growth, soreness, and darkening of the areola — usually continue. It’s common for women to have shortness of breath or to breathe faster. Increased blood flow may lead to unpleasant pregnancy symptoms, such as bleeding gums, nosebleeds, or nasal stuffiness. Pregnant women also may feel dizzy or faint because of the changes to their blood and blood vessels.
Women usually feel fetal movements for the first time during the fifth month. It may feel like flutters or butterflies in the stomach. This is called quickening.
The pregnancy symptoms of the fourth month continue this month. Heartburn, constipation, breast changes, dizziness, shortness of breath, nosebleeds, and gum bleeding are common. Breasts may be as much as 2 cup sizes bigger by this time.
Pregnancy symptoms from the fourth and fifth month usually continue. Shortness of breath may improve. Breasts may start producing colostrum — tiny drops of early milk. This may continue throughout pregnancy.
Some women have Braxton-Hicks contractions. They feel like a painless squeezing of the uterus or abdomen. This is the uterus’s way of practicing for labor and delivery. Braxton-Hicks contractions are normal and not a sign of preterm labor. But women should check with their health care providers if they have painful or frequent contractions or if they have any concerns.
A woman’s uterus continues expanding. Back pain is common. Pregnancy symptoms from earlier months continue. Dizziness may lessen.
The eighth month marks the beginning of the third trimester.
Women often start feeling tired and have a more difficult time breathing as the uterus expands up. They may get varicose veins — blue or red swollen veins most often in the legs — or hemorrhoids — varicose veins of the rectum. Hemorrhoids can be painful and itchy and cause bleeding. Women may also get stretch marks where skin has been expanded. Braxton-Hicks contractions, heartburn, and constipation may continue. Women may urinate a bit when sneezing or laughing because of pressure from the uterus on the bladder. Hormones may make hair appear fuller and healthier.
The growing fetus places more and more strain on a pregnant woman’s body. Common pregnancy symptoms continue through the end of pregnancy, including fatigue, trouble sleeping, trouble holding urine, shortness of breath, varicose veins, and stretch marks. Some fetuses drop down into the lower part of the uterus during this month. This may relieve the woman’s constipation and heartburn that are common earlier in pregnancy. But some fetuses do not drop down until the very end of pregnancy.
Many women give birth around this time.
By the end of pregnancy, the uterus has expanded from a woman’s pelvis to the bottom of her rib cage. Pregnancy symptoms in the tenth month largely depend on when the fetus drops down into lower part of the uterus in the pelvis.
Shortness of breath, heartburn, and constipation usually improve when the fetus drops. But the position of the fetus lower in the pelvis causes frequent urination and trouble holding urine.
The cervix will begin to open — dilate — to prepare for delivery. This may happen a few weeks before delivery, or it might start when a woman goes into labor. A woman may feel sharp pains in her vagina as the cervix dilates.
After the newborn is delivered, the placenta and other tissues also come out of the woman’s body. This is called the afterbirth.
Q&A with Dr. Cullins