Pregnancy Week by Week

Reviewed on 11/11/2022

What to Know About Pregnancy Week-by-Week

Picture of The Three Stages of Pregnancy
Picture of The Three Stages of Pregnancy

Pregnancy occurs when an egg is fertilized by a sperm, grows inside a woman's uterus (womb), and develops into a baby. In humans, this process takes about 264 days from the date of fertilization of the egg, but the obstetrician will date the pregnancy from the first day of the last menstrual period (280 days 40 weeks).

After the initial visit and during the first six months of pregnancy, you should see your doctor approximately once per month. Visits should be scheduled every two weeks during the seventh and eighth months and weekly during the ninth month. Electronic fetal monitoring, sequential ultrasound examinations, or admission to the hospital may also be required depending on your circumstances. Pregnancy occurs with the fertilization of a woman's egg by a man's sperm. Fertility drugs may improve a woman's odds of achieving a pregnancy.

The doctor will probably provide the woman who is pregnant with information to read regarding her pregnancy. She should ask questions if she needs help understanding the written information or what is happening during the pregnancy.

Your doctor or midwife will use certain terms when he/she talks to you about your pregnancy:

  • Intra-uterine pregnancy: A normal pregnancy occurs when a fertilized egg is implanted in the uterus (womb) and an embryo grows.
  • Embryo: The term used for the developing fertilized egg during the first 9 weeks of pregnancy.
  • Fetus: The term used for the developing embryo after 9 weeks of gestation.
  • Beta human chorionic gonadotropin (also called beta-hCG): This hormone is secreted by the placenta and can be measured to determine the presence and progression of the pregnancy. Urine or blood can be tested for its presence, and it is the hormone involved in the performance of a home pregnancy test. A positive result means a woman is pregnant; however, this test result can stay positive for several weeks after delivering a baby or following a spontaneous miscarriage.
  • Trimester: The duration of an individual pregnancy is divided into three periods called trimesters (approximately three months in duration). Each trimester is characterized by specific events and developmental markers. For instance, the first trimester includes the differentiation of the different organ systems.
  • Estimated date of delivery (EDD): The delivery date is estimated by counting forward 280 days from the first day of the woman's last period. It is also called the estimated date of confinement (EDC).

What Are the Early Pregnancy Symptoms and Signs?

Symptoms of pregnancy include:

  • Breast tenderness or discharge
  • Nausea
  • Vomiting
  • Missing a period or having an abnormal period
  • Weight gain
  • Breast enlargement
  • Nipple darkening
  • Urinating more often than usual

Fetal movement (may be perceived after 20 weeks for new mothers)

When Should You Call a Doctor or Midwife During Pregnancy?

If a woman suspects that she may be pregnant or if she has a positive home pregnancy test, she should make an appointment with a health-care professional, which could be a doctor, an obstetrician (women's health specialist), a family physician, a midwife, or a nurse practitioner. Early prenatal care is essential to insure a favorable pregnancy outcome.

A woman who is pregnant should call her healthcare professional if any of the following conditions develop:

  • Labor or rupture of membranes (leaking fluid)
  • Serious abdominal or vaginal pain
  • Bright red vaginal bleeding
  • Vomiting more frequently than three times per day or vomiting blood
  • Severely elevated blood pressure (above 140/90)
  • Sudden and rapid weight gain
  • Severe headache or visual changes
  • Severe leg or chest pain

Go to your nearest emergency department if you have any of these symptoms:

  • Fainting
  • Vaginal bleeding through more than one pad per hour
  • Having severe pain in the abdomen or shoulder or severe dizziness
  • Passing pink, gray, or white material from the vagina that does not look like a blood clot (The woman who is pregnant should take the material to the hospital.)
  • Having a bloody discharge or gush of fluid from the vagina during late pregnancy (this may indicate that the onset of labor is imminent).
  • Seizure activity but without a history of epilepsy (This may indicate eclampsia, a complication of pregnancy).
  • Having an injury, such as a fall, a blow to the stomach or pelvis, or a car accident

Lower abdominal pain late in pregnancy may indicate the onset of labor. Labor pains occur secondary to uterine contractions. A patient may attempt consumption of clear liquids or lie on her left side for a short time to determine if the contractions will resolve spontaneously. If the pain persists, her health care provider should be notified.

What Questions Should You Ask Your Doctor about Pregnancy?

Your OB/GYN or midwife should ask you these questions when you get pregnant:

  • Am I at risk for genetic diseases?
  • How much weight should I gain during pregnancy?
  • Am I gaining weight too fast?
  • How should I alter my diet (especially if she is a vegetarian or a vegan)?
  • What tests should I have and when should I schedule them?
  • Am I a high-risk patient?
  • What is my risk for cesarean birth?
  • What exercises are safe?
  • What vaccinations should I receive during pregnancy?
  • What medications may I take?
  • May we develop a birth plan?
  • Should I hire a doula?
  • Will I be allowed to have keepsake ultrasound pictures?

What Tests Confirm That You Are Pregnant?

Several tests may be conducted while a woman is pregnant.

Pregnancy tests

The woman's urine or blood may be tested.

  • Home pregnancy test: This is a urine test kit that can be purchased at a pharmacy or grocery store without a prescription. The test can indicate whether a woman is pregnant. This type of test is known as a qualitative test. It can only test for the presence of the pregnancy hormone, beta-hCG. If a doctor is considering prescribing a medication that might not be appropriate for consumption during pregnancy, one of these simple tests may be performed in the office to determine if a woman is pregnant or to make sure she is not pregnant. If the test is performed very early in a pregnancy, the hormone level may still be negative. Most current home pregnancy tests can show positive results immediately after the first missed menstrual period.
  • hCG tests: If your OB/GYN or midwife may order sophisticated tests are called quantitative hCG levels. These tests determine the hCG levels in the bloodstream. This type of test is done by drawing blood for testing. These levels indicate approximately how far along a woman is in her pregnancy. If levels of hCG do not rise as she progresses through her pregnancy, it could indicate a problem pregnancy such as an ectopic pregnancy with low levels or twins with high levels.


A doctor may use sound waves to examine pelvic structures such as the uterus, ovaries, and the embryo or fetus.

  • Transabdominal ultrasound: A conductive gel is placed on the abdomen, and a hand-held wand that emits sound waves is moved in a systematic pattern in an effort to examine the internal structures. This test requires a full bladder so that the organs in question are lifted out of the pelvis as the bladder fills. The patient may be asked to drink two to three glasses of water starting an hour prior to the test. This method works best for more advanced pregnancies when the fetus is well-developed. The physician may have a vaginal scan performed during the first trimester to make sure the pregnancy is within the uterus and to rule out an ectopic pregnancy. It is also possible to visualize the fetal heartbeat and movement, and, thus, rule out a miscarriage. The vaginal scan can also determine if there is more than one pregnancy within the uterus. During the remainder of the pregnancy, scans may be used to look for problems, assess the age and development of the fetus, check out its position within the uterus, and, between 16 and 20 weeks, determine the fetal sex. There is no risk to the woman or her developing fetus with ultrasound, and it is not uncomfortable. Ultrasound examinations aid doctors in establishing an accurate due date. The estimated date of delivery can now be predicted within two to four days if the initial ultrasound is performed early in pregnancy.
  • Endovaginal or transvaginal ultrasound: A long, thin, sound-wave wand is covered with a condom filled with conductive gel placed inside the vagina. This type of ultrasound is usually performed early in pregnancy to confirm the intrauterine location of the fetus. This type of ultrasound also gives more detail regarding the structure of the woman's cervix and early embryonic anatomy.
  • Targeted ultrasound tests: A targeted or level II ultrasound exam provides a detailed assessment of fetal anatomy. It is recommended if there are concerns for fetal problems based on other tests or history. It is usually performed by a Maternal-Fetal Medicine specialist (perinatologist).
  • Nuchal fold translucency tests: A non-invasive screening for genetic defects. A certified ultrasound technologist measures the fold at the back of the neck. Measurements are then used to calculate the risk factor for certain birth defects. It is usually done at 10 to 14 weeks gestation and offered with a blood test that also screens for birth defects.

Blood tests

  • Complete blood count (CBC)
  • Blood type, Rh status, and antibody test
  • Thyroid test (optional)
  • Urine culture
  • Sickle cell screening if you are of African American heritage
  • Syphilis tests, HIV tests, and tests for hepatitis B
  • Alpha-fetoprotein tests or Quad Screen Test: A Quad Screen looks for four specific substances, Alpha-fetoprotein, human chorionic gonadotropin, Estriol (an estrogen), and Inhibin-A (a protein produced by the placenta and ovaries).

Culture tests

  • Gonorrhea culture (GC) and chlamydia testing
  • Group B streptococcal test between 35 and 37 weeks of pregnancy
  • Test for bacterial vaginosis (BV), candida, and trichomonas - these are performed as needed if the woman has vaginal discharge, burning with urination, or itching around the outside of the vagina.

What Can You Do at Home to Have a Healthy Baby?

  • Eat small, frequent meals throughout the pregnancy. Eat a balanced diet. Expect to gain between 25 to 35 pounds if you are of normal weight. Expect to gain less weight if you are obese (approximately 10 to 15 pounds).
  • Do not discontinue prescribed medications or initiate non-prescription medications without consulting a physician, but also consult with a doctor before taking any nonprescription medications.
  • Ginger capsules (available as an over-the-counter option) may help with nausea in pregnancy, sometimes called morning sickness. Talk with a doctor about other options.
  • Do not smoke, drink alcohol, or use illicit drugs.
  • Continue to exercise with normal routines unless the doctor advises otherwise. Stay hydrated during exercise sessions.
  • It is OK to have sexual intercourse while you are pregnant if you don't have any complications. If you aren't sure, ask your OB/GYN or Midwife.

What Monitoring May Be Necessary During Your Pregnancy?

  • Electronic fetal monitoring: Sometimes late in pregnancy, a woman who is pregnant may be placed on a fetal monitor to verify the health of the fetus or to see if the woman is in early labor.
  • Biophysical profile test: This is a noninvasive test that uses ultrasound to assess whether or not the baby is receiving an adequate supply of oxygen. It is typically performed during high-risk pregnancies or if a woman has gone past her due date.

What Medications Are Safe to Take if You Are Pregnant?

Because some medicines are not safe to take during pregnancy, it is important that a woman take only those that have been approved by her doctor. If anyone tries to prescribe a new medicine, the woman should explain that she is pregnant and ask if the drug is safe. The FDA previously listed five categories of pharmaceutical labeling for drugs that might be used during pregnancy.

A doctor or pharmacist can provide advice on the safety level (indicated by category) of medications before a pregnant patient begins their usage. Doctors will often use category B and C medications (see the following list) if it is felt that the potential benefit of the product outweighs any risks. Few conditions during pregnancy can be treated adequately with category A medications. The FDA categories were instituted in 2015. 

  • Category A: Safety established using human studies
  • Category B: Presumed safety based upon animal studies
  • Category C: Uncertain safety with animal studies showing an adverse effect
  • Category D: Unsafe with evidence of risk that may, in certain clinical circumstances, be justifiable
  • Category X: Highly unsafe with risk or use outweighing any possible benefit

What Are Potential Complications During Pregnancy?

A pregnant woman and her doctor will monitor the pregnancy to exclude or prevent certain pregnancy conditions. The physician will also treat non-pregnancy-related medical conditions in such a way as to promote the appropriate physical and neurological development of the fetus. Conditions of particular importance include:

  • High-risk pregnancy: If you are considered prone to certain complications during pregnancy, you will be classified as high-risk. Examples include pregnancies in women with diabetes and/or high blood pressure. Age-related complications can occur in women such as teenagers, women who are over the age of 35, or those who have been treated for infertility and have pregnancies resulting from the use of assisted reproductive technology.
  • Ectopic pregnancy: This is a pregnancy in which the egg implants somewhere other than the uterus. This complication can be life-threatening. Ectopic pregnancy must be diagnosed early to avoid damage to the fallopian tubes and to prevent serious maternal illness or death. It is also called tubal pregnancy (if the egg implants in the fallopian tubes) or extra-uterine pregnancy.
  • Cervical incompetence: This is a condition in which the cervix begins to open (widen) and/or efface (thin) without contractions before the pregnancy has reached term. Cervical incompetence can be a cause of mid-pregnancy miscarriage.
  • Preterm Labor: In this condition, the uterus begins to contract before the baby has reached full term.
  • Preeclampsia/eclampsia: Preeclampsia is a systemic disease that can affect various organ systems. Vascular effects cause blood pressure to rise in a pregnant woman. The condition may cause kidney damage, generalized swelling, hyperactive reflexes, as well as deleterious abnormalities in blood chemistry and nerve reflexes. If left untreated, preeclampsia can proceed to eclampsia, a serious condition that may result in seizures, coma, and even death.
  • Multiple gestations (for example, twins and triplets): Preterm births are twice as likely in twin pregnancies as in single pregnancies. The percentage of preterm birth is even greater for triplet pregnancies and higher-order pregnancies. Preeclampsia is also seen three to five times more frequently with multiple gestations.

What Birth Control Methods Prevent Pregnancy?

Contraception refers to methods used to prevent pregnancy. There are many ways to prevent pregnancy, but none of them is 100% effective with the exception of abstinence. Methods of contraception can vary widely in their effectiveness:

What Factors Determine the Outcome of You and Your Baby's Health?

Many events determine the outcome of a pregnancy.

  • Maternal weight gain: The amount of weight a woman gains when pregnant can be important in predicting the outcome of pregnancy. Excess weight gain places a woman who is pregnant at risk for diabetes and hypertension, and it may increase the chance of needing a cesarean birth (C-section). Too little weight gain places the infant at risk for intrauterine growth restriction and the mother at risk for anemia, nutritional deficiencies, and osteoporosis.
  • Nausea and vomiting: Even if a pregnant patient experiences what seems like an abnormal amount of nausea and vomiting (morning sickness), it probably will not affect the baby's health, particularly if the woman is still gaining weight at the anticipated rate.
  • Low or high red blood cell counts: The normal red blood cell count range varies slightly between laboratories, but is generally 4.2 - 5.9 million red cells per microliter. The risk of delivering prematurely is increased if the woman's blood count is low (anemia). Low blood counts also put her at risk of requiring a transfusion following a delivery. If the woman's blood count is too high (polycythemia), her baby may be larger than expected.
  • Maternal obesity: A person with a body mass index (BMI) over 30 is considered obese. If a woman who is pregnant is obese and has diabetes, her baby is three times more likely to have a birth defect. If she is obese but does not have diabetes, the risk of birth defects is not increased.
  • Maternal age: If the pregnant patient is older than 35 years, her infant is at a higher risk of birth defects and complications. The focus of genetic screening is to enable the woman to understand any problems her newborn may have. There is a 2% to 3% rate of major birth defects in this population.
  • Folic acid deficiency: A pregnancy that is deficient in the nutrient folic acid, also known as folate, can lead to neural tube defects such as spina bifida in the fetus. Neural tube defects are malformations of the brain and spinal cord which typically occur within the first few weeks of pregnancy; therefore, folic acid supplementation should be taken prior to conception and throughout the course of the pregnancy. It is recommended all non-pregnant women take a daily supplement containing 400mg of folate and pregnant women should take a supplement with 1000mg of folate.
  • DHA deficiency: During pregnancy, a diet that is deficient in the omega-3 fatty acid docosahexaenoic acid (DHA) can lead to inadequate development of the eyes, brain, and central nervous system of a fetus. It is recommended that pregnant and lactating women consume 300mg of DHA per day. DHA is found in animal meats, fish, eggs, and vegetable oils.
  • Omega-3 fatty acid deficiency: Having an Omega-3 deficiency during pregnancy can be harmful to both the mother and the baby. Omega-3 is a polyunsaturated fat that supports the growth and development of a fetus and helps reduce the risks of pregnancy complications. It is recommended women consume 300mg of Omega-3 daily during the course of pregnancy. This nutrient can be found in cold-water fish, eggs, walnuts, and dark green leafy vegetables.

Health Solutions From Our Sponsors

Woman having pregnancy test

Pregnancy Test

Positive Home Pregnancy Test

For most home pregnancy tests, you either hold a test strip in your urine stream as you urinate into the toilet or you collect your urine in a clean cup and dip your test strip into the cup. The test usually takes only a few minutes.

  • Some tests are able to detect low levels of hCG, indicating pregnancy. For the most reliable results, test 1-2 weeks after you have missed your period.
  • You can improve your chances for an accurate result by using your first morning urine for the test.
  • If you think you are pregnant, but your first test was negative, you can take the test again after several days.
  • The home pregnancy test and the urine pregnancy test used by your health-care professional are similar. Both can detect hCG, but your provider is probably more experienced in running the test.
Reviewed on 11/11/2022
Smith, JA, PharmD, et al. Patient information: Morning sickness (The Basics). UpToDate. Last reviewed: Jan 2019.

Ockwood, CJ, MD, et al. Initial prenatal assessment and first-trimester prenatal care.