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Pregnancy, or gestation, is a period of around 9 months when an unborn baby is developing in the uterus. The first sign of pregnancy is usually missed menstruation, but there are also other signs.

Pregnancy involves changes that will significantly affect a woman's body. Most pregnancies last for about 280 days, but they can last anywhere from 37 to about 42 weeks, starting from the first day of the last period.

Doctors divide pregnancy into three stages, or trimesters, during which specific changes occur. Each trimester lasts for around 3 months.

A pregnancy calculator can help to predict when a baby is likely to be born.

Read on to learn more about what to expect during pregnancy.

Nausea is an early signShare on Pinterest
Nausea is common in early pregnancy.

Apart from missing a period, other early signs of pregnancy include:

  • nausea, with or without vomiting
  • tiredness
  • dizziness
  • breast changes, such as tenderness
  • frequent urination

Nausea is common during the first 3–4 months of pregnancy, while many women experience tiredness during the first and last trimester.

To confirm a pregnancy, a woman can:

  • see a doctor
  • take a home pregnancy test

A pregnancy test detects the human chorionic gonadotropin (HCG) hormone in the blood or urine. HCG is present just a few days after becoming pregnant.

Levels of the hormone are low at the beginning of pregnancy, and they gradually increase. Having a high level of HCG can signal multiple pregnancies, for example, having twins or triplets.

If a home pregnancy test is positive, see a healthcare professional for confirmation. They can provide this by conducting an abdominal or transvaginal ultrasound scan.

The scan can confirm:

  • the gestational age of the pregnancy
  • how many embryos there are
  • whether the placement is correct in the womb

The doctor can also ensure that a woman receives proper advice and support from the start of pregnancy.

After confirming the pregnancy, the healthcare professional often recommends taking a multivitamin supplement that contains folic acid. If the pregnancy is planned, the doctor may recommend taking folic acid ahead of conception.

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A home pregnancy test can show if a woman is pregnant, but a doctor should confirm the result.

Conception occurs when sperm from a male penetrates an egg from a female and fertilizes it. This usually happens in the woman's fallopian tube after ovulation. The result is a zygote — a unified sperm and egg cell.

The zygote immediately starts to divide, forming a cluster of cells called an embryo.

After 5–7 days of dividing and growing, the embryo attaches to the wall of the womb, or uterus, and puts out root-like veins called villi. This process is called implantation.

The villi ensure that the embryo is anchored to the lining of the uterus. They will eventually become the placenta, which feeds and protects the embryo or fetus as it develops, supplying it with oxygen and nutrition, and expelling waste.

Home pregnancy testing kits are available for purchase online.

The first trimester runs through the first 12 weeks. The embryo develops quickly at this stage.

A woman will probably experience:

  • tiredness
  • nausea
  • breast tenderness
  • an increase in urination, due to hormonal changes and increased blood flow through the kidneys

During this time, the fetal bones, muscles, blood, nervous system, and most of the internal organs start to form.

When these are complete, the embryo is known as a fetus.

By this point, the fetus measures about 1 inch in length, the ears and facial features are evident, and the fingers and toes are starting to appear.

The fetus develops inside the uterus, surrounded by amniotic fluid. This is the "water" that "breaks" just before delivery.

Toward the end of the first trimester, the doctor will recommend some tests, including follow-up ultrasound scans, to check on the baby's health and development.

The second trimester lasts from week 13–28. The pregnant woman will gain weight and develop extra reserves of fat.

She will be able to feel the movements of the fetus, and others can often feel them by placing a hand on the woman's abdomen. Movement may also be visible.

Many women feel more comfortable in the second trimester. Nausea usually ceases, and energy levels are often higher.

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During the third trimester, antenatal classes will prepare you for what to expect during labor and after delivery.

The third trimester lasts from week 29 until birth. The baby will build up stores of fat, and the lungs and senses of hearing, taste, and sight will develop further.

The woman may experience back pain and find it more difficult to rest comfortably. She will also urinate more often, due to the pressure on her bladder. In addition, indigestion can result when the fetus pushes against the stomach.

Early contractions can occur days or weeks before birth, and doctors call these Braxton–Hicks contractions. They do not indicate labor.

Many hospitals offer antenatal classes, which provide information about giving birth and how to care for a newborn, including tips on breastfeeding.

It is important to keep in touch with healthcare providers throughout pregnancy.

The first visit

The initial appointment usually occurs within the first 12 weeks of pregnancy.

A doctor will take note of the woman's general health and any issues that may require care or treatment. They will also advise about healthful living during pregnancy.

A healthcare provider will describe local pregnancy care services and any available financial assistance.

They will weigh the woman, check her blood pressure, and test her urine for signs of infection and other abnormalities. They may also perform a physical exam and Pap smear.

Also, a doctor usually recommends an ultrasound scan. This scan uses sonic waves to produce an image of the fetus and predict the birth date. It can also show if there are multiple pregnancies.

Further visits and tests

A second ultrasound scan may take place between weeks 18 and 20 to confirm whether the baby is developing correctly.

Some tests can show whether a woman has a condition that may affect her health or that of the fetus.

These conditions include:

Anemia: A woman may need more iron during pregnancy to produce hemoglobin, a protein in red blood cells that carries oxygen to other cells. Having anemia, a red blood cell deficiency, can complicate this process.

Down syndrome: The risk increases with the woman's age. Simple blood tests can screen for this and other conditions as early as 9 weeks' gestational age. An amniocentesis test can also evaluate for chromosomal abnormalities.

Hepatitis: Hepatitis B and C can pass from the woman to the baby. Working with a healthcare provider can reduce the risk to the baby during pregnancy, at delivery, and after birth.

Rubella (German measles): The risk of transmission is very small, but it can lead to miscarriage, genetic abnormalities, or similar developmental problems.

HIV: Medications can prevent the transmission of the virus to the baby during pregnancy, labor, delivery, and breastfeeding.

Syphilis: If a woman does not receive treatment, this infection can seriously harm herself and the baby.

Gestational diabetes: This develops during pregnancy and often resolves after delivery. It has few symptoms.

At the beginning of pregnancy, it is important to talk with a healthcare professional about any existing conditions or symptoms, including headaches, blood pressure issues, diabetes, and thyroid conditions. It is also a good idea to bring up prior surgeries.

Common causes of discomfort during pregnancy include:

Anemia is also a common issue, and many women take iron supplements to prevent it.

When to see a doctor

Some complications of pregnancy require medical intervention.

Miscarriage refers to the loss of a pregnancy. It usually happens during the first trimester. The first sign is vaginal bleeding, which can occur with abdominal or back pain.

Ectopic pregnancy occurs when the embryo implants somewhere other than the lining of the uterus. It can lead to significant internal bleeding and is potentially fatal for the woman.

Symptoms may include:

  • pain at the tip of the shoulder
  • vaginal bleeding
  • pain on one side of the abdomen
  • pain when urinating or passing stools

The doctor will usually diagnose an ectopic pregnancy during the first semester.

Preeclampsia involves high blood pressure, either during pregnancy or just after delivery. It can be dangerous for both the woman and the baby.

Symptoms include:

  • swelling in the face, hands, feet, and ankles
  • rapid weight gain
  • vision problems
  • abdominal pain
  • headaches

If any of the symptoms above occur, including a rise in blood pressure, the woman should seek urgent medical attention.

Placenta previa happens when the placenta covers part or all of the cervix, which is the passage through which the baby leaves the uterus. This issue usually resolves on its own. If it does not, a cesarean delivery may be necessary.

Obstetric cholestasis occurs when bile builds up in the blood. It can lead to preterm birth or stillbirth, and it usually causes severe itchiness in the woman's hands and feet.

Molar pregnancy happens when the sperm fertilizes the egg, but a genetic problem prevents the embryo from developing. The result is usually pregnancy loss. In some cases, this can be dangerous to the woman.

Preterm birth is when a baby is born too early. The earlier the birth, the higher the risk of complications, as the newborn's systems may not have developed sufficiently to survive outside the womb. However, medical advances can support the care of these babies, many of whom grow up to lead full, healthy lives.

Stillbirth describes a baby born after 24 weeks of pregnancy without signs of life.

It is not always possible to avoid the complications of pregnancy, but the following strategies can help reduce the risk:

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Exercise can contribute to a healthy pregnancy.

Keep physically active to maintain general health and body weight and to help with labor and delivery. Walking and swimming are often suitable activities, and doctors tend to warn against playing contact sports.

Avoid excessive weight gain, beyond what is necessary. A woman with obesity, for example, should not gain large amounts of weight during pregnancy. A doctor can advise about how much weight gain is suitable.

Avoid tobacco smoke, as exposure increases the risk of disease in later life. Also, avoid exposure to air pollution as much as possible.

Avoid alcohol, as it can cause fetal alcohol syndrome.

Avoid marijuana, or cannabis, as the drug may have harmful effects on the fetus.

Take vitamins and supplements exactly as the doctor advises. They will usually recommend folic acid, which can benefit the fetus. Avoid vitamin A supplements and check about the possible risks and advantages of taking other supplements and remedies.

Discuss any medications with a healthcare professional before using them.

Follow a healthful and balanced diet, with plenty of fruits, vegetables, and whole grains

Consume plenty of fluids, at least 2 liters a day, preferably of water.

Reduce caffeine to less than 200 mg per day, as recommended by The American College of Obstetricians and Gynecologists.

Avoid fish that may contain high levels of mercury, especially shark, marlin, swordfish, and barracuda.

Avoid raw meats, raw fish, and some cheeses: Some bacterial infections from food, especially salmonella and listeriosis, can harm the fetus. These can come from cured, uncooked, or undercooked foods and cheeses ripened with mold, such as Camembert.

Take care with soil: Soil and some animal feces can transmit infections. Toxoplasmosis from cat feces, for example, can severely harm the fetus. It is important to wear gloves and wash the hands before and after gardening or changing cat litter.

At or after 39 weeks' gestation, the baby's development is usually complete. If a pregnancy lasts for 42 weeks, a doctor will probably induce the birth.

Some women give birth at home. However, it may take longer to access medical assistance. Anyone considering a home birth should discuss it with a healthcare professional, who will make individual recommendations.

When the time comes to deliver, a woman may have a choice of pain reliever.

Also, some hospitals offer the use of a birthing pool, in which delivery takes place in water. Otherwise, a doctor may recommend using a warm bath to help relieve pain, but advise delivering out of the water. These are both safe options, as long as a medical professional supervises them.

It is important to discuss all delivery options with a healthcare professional and to follow their instructions.

Pregnancy can be an exciting time marked by significant changes.

To reduce the risk to the fetus, it is important to avoid using alcohol, tobacco, and similar substances.

Discuss any new or unusual symptoms that arise during the pregnancy with a doctor. Call a healthcare professional right away if any vaginal bleeding occurs. Also, talk with the doctor about precautions during each trimester.

Keeping in touch with healthcare professionals can provide key support throughout pregnancy.

For more information, see our week by week series on pregnancy, starting with fertilization.