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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 others.

Most pregnancies last for about 280 days, which is somewhere around 40 weeks. A pregnancy calculator can help predict when a baby is likely to be born.

This article discusses what to expect for the duration of pregnancy from conception to delivery, including the common symptoms, potential complications, as well as tests and medical exams.

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One of the most common early signs of pregnancy is a missed menstrual cycle. According to the American Pregnancy Association, 29% of pregnant women have reported this as their first sign of being pregnant.

Other than a missed period, signs of pregnancy that may occur from the first few weeks of conception include:

  • nausea, with or without vomiting
  • tiredness
  • dizziness
  • breast changes such as tenderness
  • frequent urination due to hormonal changes and increased blood flow through the kidneys
  • light implantation bleeding or spotting
  • fatigue

Not all pregnant people experience the same symptoms and some experience no symptoms at all.

Confirming a pregnancy

To confirm a pregnancy, a person can:

  • see a doctor for a physical exam and a blood pregnancy test
  • 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 a multiple pregnancy, such as when a person is pregnant with twins or triplets.

If a pregnancy test is positive, a person can get 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

Home pregnancy testing kits are available for purchase online.

Doctors measure the fetal age of the baby from the date of conception. But they may determine a pregnant person’s due date by looking at the gestational age, which they measure by counting the pregnancy from the first day of the person’s last menstruation. This includes the period of ovulation and conception.

The following guide follows the gestational age measurement of pregnancy. For more detailed information, see our more thorough series on what to expect during pregnancy week by week.

Weeks 1-13

The first trimester runs through the first 13 weeks, including the period of ovulation and conception.

Conception and implantation

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

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

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

Occasionally, the embryo implants somewhere other than the lining of the uterus, usually in the fallopian tube. This results in an ectopic pregnancy.

When the embryo implants normally, 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 as it develops, supplying it with oxygen and nutrition, and expelling waste.

Early development

The embryo then begins to develop quickly. The first things to develop are the heart, spinal cord, brain, and gastrointestinal tract. The placenta begins to form. As time goes on, more structures and organs grow. By week 6, a doctor may be able to detect a heartbeat.

By week 7, most essential organs are already forming. By week 8, everything that adult humans have both inside and out is present in the embryo in a much smaller form.

By week 9, the embryo becomes a fetus and continues to develop inside the uterus, surrounded by amniotic fluid. This is the “water” that “breaks” just before delivery. By the end of this stage, the fetus will grow to about 3 inches (in) in length and a weight of about 1 ounce (oz).

Symptoms to expect

In the first 13 weeks, the symptoms of pregnancy will likely be similar to those that may occur at the earliest stages, but they may increase as time goes on.

Additional symptoms a pregnant person may encounter at this time include mood swings, changes in appetite or cravings for certain foods, constipation, headaches, and heartburn.

While some pregnant people may gain weight at this stage, others may lose weight. Not all people experience these symptoms, as every pregnancy is different.

Weeks 13-28

In the second trimester, the fetus forms a type of fine hair called lanugo on its head. It also begins to suck and forms fingerprints.

The sweat glands, eyebrows, eyelashes, and eyes begin to form. The brain, the nervous system, and other essential organs continue to develop.

By week 22, if a fetus is born, it may be able to survive with medical intervention. By week 28, the fetus will grow to about 2 ¼ pounds (lbs) in weight and a length of 14 in.

Symptoms to expect

In the second trimester, pregnant people will usually begin to gain weight. They may begin to feel the movements of the fetus, and others can often feel them by placing a hand on the pregnant person’s abdomen.

Many pregnant people feel more comfortable in the second trimester. Nausea usually stops, and energy levels are often higher. Some people may still experience some discomfort. This may include back pain, carpal tunnel syndrome, itching on the palms of hands or soles of feet, and swelling of the face, fingers, or ankles.

If the swelling is sudden or severe, or if the itching goes along with vomiting, nausea, jaundice, fatigue, or loss of appetite, a person should check with a doctor. These may be signs of preeclampsia or a problem with the liver.

Some people may also notice some discoloration of the skin and may begin to see stretch marks.

Weeks 29-40

The third trimester lasts from week 29 until birth, which is commonly week 40. In the first few weeks of this period, the fetus will really grow in size. It will begin to make some rhythmic breathing movements with its lungs, although these are still developing.

The bones develop fully by this time, but they are still soft. The eyelids will open. After week 33, the fetus will usually make its way into a head-down position in preparation for birth. It will continue to gain more weight and lose its lanugo hair.

From 38 weeks the fetus is considered full-term. It may weigh anywhere from 6 ¾ to 10 lbs with a length of about 16-19 in.

Symptoms to expect

Many of the same symptoms from previous weeks may continue during this time. A pregnant person may experience increased back pain and find it more difficult to rest comfortably. They may urinate more often, due to the pressure on the bladder. In addition, indigestion can result when the fetus pushes against the stomach.

Additional symptoms may include things like hemorrhoids, shortness of breath as the baby presses on the diaphragm, and insomnia.

Some people may find that their breasts are leaking colostrum, a pre-milk substance that the body produces in preparation for milk production.

Early contractions may also occur days or weeks before birth. Doctors call these Braxton–Hicks contractions. They do not indicate labor.

Throughout pregnancy, a person will have regular check-ups and tests to ensure that the baby is developing properly.

The first visit

The initial appointment usually happens around or after the eighth week of pregnancy. The doctor may confirm a person’s pregnancy with an ultrasound, perform a pap smear, and take cervical cultures. The ultrasound will show if there are multiple pregnancies.

The doctor will also gather a person’s detailed medical history and do a physical exam. This includes taking a person’s blood pressure and doing a urine test for signs of infection and other abnormalities.

Another part of the first visit is to send a pregnant person for blood work to check their blood type and test for a variety of diseases such as HIV and hepatitis. A doctor may also do screening for a number of genetic disorders that can impact the developing embryo.

At this time the doctor will answer any questions the person may have and give the person recommendations about safe foods during pregnancy, prenatal vitamins, exercise during pregnancy, safe medications during pregnancy, and other things the person should know.

Further visits

After the first visit, a pregnant person can expect to see a doctor monthly for the first 28 weeks. Between weeks 28 and 36, a person will come in every two weeks. From week 36 until birth, the visits become weekly. People whose pregnancies are high risk may need to come in more often.

In the later visits, the doctor may:

  • check a pregnant person’s blood pressure
  • measure a pregnant person’s weight gain
  • measure the abdomen to check how the fetus is growing
  • toward the end of pregnancy, check the position of the baby in preparation for birth
  • do more blood or urine tests
  • do additional ultrasounds

Common tests

Most pregnant people have to undergo a number of screening tests throughout pregnancy. Some people may have to do additional tests if they have high-risk pregnancies or additional medical conditions.

The most common tests include:

  • First-trimester screen: Taking place between 11 and 14 weeks, this screens for chromosomal disorders such as Down syndrome and trisomy 18, as well as things like heart defects.
  • 20-week ultrasound: Many pregnant people will have an ultrasound around week 20 to check the development of the fetus. The doctor will look for any abnormalities and will be able to reveal the sex of the fetus to those who request it.
  • Urine test: Often during a check up, a pregnant person will have to do a urine test to screen for things like a urinary tract infections, diabetes, or preeclampsia.
  • Glucose test: Taking place between weeks 26 and 28, this screens for gestational diabetes. A person will need to consume a sugary drink and wait one hour to determine blood sugar levels.
  • Group B streptococcus test: Taking place between weeks 36 and 37, this screens for a bacteria that may pass to babies during birth and can lead to a serious infection.

Precautions

During pregnancy, doctors will advise a pregnant person to be careful about or avoid a number of things for the entire duration of pregnancy.

  • Smoking: This increases the risk of preterm labor and birth defects.
  • Alcohol: There is no safe amount of alcohol a person can consume during pregnancy. Drinking alcohol puts the baby at risk for birth defects and fetal alcohol syndrome.
  • Drugs: Marijuana and others drugs raise the risk of pregnancy complications and birth defects in the baby.
  • Overheating: Overheating increases the risk of a neural tube defect. Pregnant people should be careful in hot weather and treat fever quickly.
  • Fish: Pregnant people should not eat fish that are high in mercury like bigeye tuna or king mackerel.
  • Raw food and meats, soft cheeses if they are unpasteurized, deli meats, sprouts, and prepared salads like chicken salad: Pregnant people should avoid eating these foods to reduce the risk of contracting bacterial infections like salmonella and listeriosis, which can harm the fetus.
  • Certain medications: Not all medications, including over-the-counter and prescription medications, are safe to take in pregnancy. Some may be safe to take only after week 13. A person should check with their doctor before taking any medications.
  • Soil: Soil and some animal feces can transmit infections. Toxoplasmosis from cat feces, for example, can severely harm a fetus. It is important to wear gloves and wash the hands before and after gardening or changing cat litter.
  • Caffeine: Pregnant people should consume less than 200 mg of caffeine per day, as recommended by the American College of Obstetricians and Gynecologists.

In addition to typical pregnancy symptoms, people who are pregnant may experience additional things that may require medical attention. This includes things like dental problems, urinary tract infections, and anemia. A person can get basic medical treatments for these kinds of conditions.

In some cases, however, a complication can be serious. Examples include:

  • Hypertension: This is a term that describes high blood pressure. A person will need to be monitored and may need medication to control this, as high blood pressure puts a pregnant person at risk for preeclampsia.
  • Preeclampsia: When this happens, a pregnant person’s high blood pressure reduces a fetus’s blood supply. If doctors do not treat it in time, the person can develop eclampsia, which can cause seizures and lead to a coma.
  • Gestational diabetes: This is when a person who didn’t have diabetes before develops it during pregnancy. If doctors do not control it, it can cause high blood pressure, which can lead to preeclampsia.
  • Infections: If a person contracts an infection during pregnancy, including some sexually transmitted infections (STIs), they may be at risk for miscarriage, preterm labor, and stillbirth. The baby may be at risk for developing birth defects.
  • Placenta previa: This happens when the placenta covers part or all of the cervix, which is the passage through which the baby leaves the uterus. This issue may resolve on its own. If not, a person will need a cesarean delivery.

It is not always possible to avoid the uncomfortable symptoms of pregnancy, but the following strategies may help:

  • Keep physically active: Exercise to maintain general health and body weight and to help with labor and delivery. Walking and swimming are often suitable activities. Doctors tend to warn against playing contact sports.
  • Maintain a healthy weight: “Eating for two” does not mean that a pregnant person should eat twice as much. Although gaining weight during pregnancy is normal, doctors recommend that pregnant people gain about 2-4 pounds in the first trimester, and about 3-4 pounds in the second and third trimesters. A person’s whose body mass index (BMI) is already high may want to consult with a doctor, as they may need to gain less weight during their pregnancy.
  • Follow a healthy and balanced diet: This means eating plenty of fruits, vegetables, and whole grains in sensible portions.
  • Take vitamins and supplements: Take these exactly as the doctor advises. Doctors commonly recommend folic acid, calcium, vitamin D, as well as a number of other supplements. Some vitamins, like vitamin A, may be unsafe for the baby if taken at doses that are too high. A person can purchase prenatal vitamins in any pharmacy or online.
  • Consume plenty of fluids: Doctors recommend pregnant people drink at least 2 liters a day, preferably of water.

When a pregnant person is ready to deliver, there will be some signs. These may not be the same for every person. They may include:

  • Lightening: If it suddenly becomes easier to breathe, it may mean that the baby has dropped low in preparation for birth.
  • Mucus plug: The body may expel the plug that protects the cervix from bacteria. It may appear clear, pink, or a bit bloody. It could look a bit like a cork. It is sometimes referred to as the “bloody show.”
  • Water breaking: This is when the amniotic sac bursts and the fluid leaks out. 1 in 10 women will experience this as a big burst. In many cases it may be just a small trickle.
  • Effacement: This is when the cervix stretches and thins in the last month before labor.
  • Dilation: When the cervix begins to open in preparation for birth.
  • Contractions: There are different types of contractions. Braxton-Hicks contractions are just practice contractions. They are irregular and do not indicate labor. However, if the contractions are regular, predictable, and begin to get closer together and last longer, this may indicate labor.

Stages of labor

The labor experience is different for every person. In general, when a person undergoes a vaginal birth, labor consists of several stages:

  • Early labor: This stage lasts about 8-12 hours until the cervix dilates to 3-6 cm. Usually, the contractions are mild. They may last about 30-45 seconds with 5-30 minutes of rest in between.
  • Active labor: This stage lasts about 3-5 hours until the cervix dilates to 7 cm. People who get an epidural may stay longer in this stage. Contractions will usually last 45-60 seconds with a 3-5 minutes rest in between. They may be more intense.
  • Transition: This stage lasts about 30 minutes to 2 hours, or until the cervix dilates to 10 cm. Contractions will be longer and more intense. They may last 60-90 seconds with 30 second-2 minute breaks.
  • Pushing: Generally, the pushing stage can last from 20 minutes to 2 hours. Contractions continue and last 5-90 seconds with breaks of 3-5 minutes. With the contractions, a person will feel a strong urge to push. The baby’s head will begin to come out, which is known as crowning. A person may feel a burning sensation. The doctor will advise the person to stop pushing and then the baby will be born.

Pregnancy can be an exciting time marked by significant changes. It is also a time when the body experiences a variety of symptoms. Knowing what to expect during pregnancy can help a person cope with the many changes and know what to do at every stage.

To reduce the risk of more serious symptoms or complications, it is best to have a medical professional monitor a pregnancy and follow all medical recommendations.

Discuss any new or unusual symptoms that arise during the pregnancy with a doctor.

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