Your Pregnancy

The Stages of Pregnancy

The average pregnancy lasts about 40 weeks, as timed from the first day of your last menstrual period. If you have regular monthly periods, the date you became pregnant is usually about two weeks after the first day of your last menstrual period.

The stages of pregnancy are divided into three trimesters. Each trimester lasts about three months, or 14 weeks. Each stage is described in terms of weeks. For example, a “33 and 2/7 weeks” pregnancy indicates that the woman is 33 weeks and 2 days into her pregnancy. The following outlines the common breakdown:

• First trimester: 0 - 13 and 6/7 weeks (months 1- 3)
• Second trimester: 14 - 27 and 6/7 weeks (months 4 - 6)
• Third trimester: 28 - 40 and 6/7 weeks (months 7 - 9)

For more information, see our prenatal care timeline.

Determining Your Baby’s Estimated Due Date

You will find out the estimated due date of your child at your first prenatal visit. Your care team will use a combination of information to determine your most accurate due date. Only about 1 in 20 women actually deliver on their estimated due dates. However, the estimated due date helps your health care team track your baby’s gestational age so we can monitor and record your baby’s growth. The estimated due date also helps your care team create a schedule for tests needed during your pregnancy.

Your Healthy Pregnancy

One of your responsibilities while pregnant is to take good care of your health. Having a healthy lifestyle can help you feel more comfortable as your body changes. Even more important, staying healthy can help reduce the chances of you or your baby having serious medical problems. Here are some of the most important things to think about before and while you are pregnant.

Your OBGYN provider will guide you through your pregnancy. It is important to make and keep all appointments recommended by your obstetrician or certified nurse midwife. This includes office appointments and any testing.

Diet and exercise

Eating a healthy diet before and during pregnancy boosts your health and is essential to help your baby grow. Exercising regularly and maintaining a healthy body weight is also important before and during pregnancy. Your doctor or midwife can let you know your ideal pregnancy weight. Overweight birthing parents risk developing medical problems such as high blood pressure and diabetes. Underweight birthing parents may deliver low-birth-weight babies. See Nutrition and Exercise for more details.

Daily vitamins

Your doctor or midwife will recommend daily prenatal vitamins. These vitamins give you enough nutrients to properly nourish your baby. Before you become pregnant, it is a good idea to start taking prenatal vitamins that have Folic acid. Folic acid 400 micrograms (mcg) per day helps decrease the risk of your baby having neural tube defects (spina bifida). See Nutrition for more details.

Ongoing health conditions

If you have a health condition, such as diabetes or high blood pressure, it could affect your pregnancy. Please talk to your health care provider about keeping medical issues under control.

Prevent infection

Don’t eat undercooked meat, deli meat, unpasteurized dairy or raw eggs while you’re pregnant. These foods could contain dangerous bacteria or parasites. You should also avoid all contact with cat droppings and cat litter while pregnant. Flies and other insects in contact with cat droppings can carry infections. Droppings and litter can contain a parasite that can make your developing baby seriously ill or even cause death. Make sure your vaccines are up-to-date, including seasonal flu, COVID-19 and whooping cough (Tdap). See Nutrition, Tdap Vaccine and Group B Strep Screening for more information.

Harmful substances

Do all you can to avoid exposure to toxic and chemical substances, such as lead and pesticides. Exposure to these could damage your baby’s health. If any imaging that uses ionizing radiation is needed (such as X-rays or CT scans), please talk to your health care provider about any possible risk to your baby. This does not include ultrasounds, which are safe during pregnancy.

Domestic violence

Birthing parents whose partners physically abuse them before they are pregnant have an increased risk of violence during pregnancy. Have a plan to protect yourself and your baby. Your doctor or midwife is ready and willing to help you find resources to deal with domestic violence. For additional support, please visit the National Domestic Violence Hotline.

Avoid alcohol and drugs

Drinking alcohol, smoking (including marijuana) or taking drugs while pregnant can greatly harm your baby’s health. Please let us know if you have been using any substances so far during pregnancy. We’re happy to provide you with resources to help you stop. Also, tell your health care team about any medications (prescription and over-the-counter) that you take. Some medicines are not safe for your developing baby.

Stop smoking

Birthing parents who smoke are more likely to have premature and low birthweight babies. Both of these factors can increase your baby’s chance of having long-term medical problems. Babies exposed to tobacco smoke are more likely to die from sudden infant death syndrome (SIDS) than babies who are not exposed. Even being exposed to secondhand smoke (from someone physically near you who smokes) can increase your chance of having a low birthweight baby.

There are also dangers from “third-hand” smoke — tobacco particles, chemicals and gasses left on hair, clothing and furniture. Please talk to your care team about ways to stop smoking. The California Smokers' Helpline (1-800-NO-BUTTS) is a free service to help people quit smoking.

Ask us for help

If you have questions about these topics or any other issues, please talk to your UCLA Health care team. We want to help you have a healthy, happy pregnancy.