Pregnancy

Pregnancy is the period during which a fertilized egg develops into an embryo and then a fetus. It usually develops inside the uterus, also called the womb.

Pregnancy is not a disease. It is a major biological process that changes how the body works and affects healthcare needs. Some medical conditions can begin during pregnancy, and existing conditions may need different monitoring or treatment.

Healthcare professionals usually date a pregnancy from the first day of the last menstrual period. This is about two weeks before fertilization in a typical cycle, although cycle length and ovulation timing differ. A full pregnancy is often described as lasting about 40 weeks from that date.

Pregnancy is commonly divided into three trimesters. The exact week used to separate each trimester may differ slightly between health systems.

A due date is an estimate, not a deadline. It may be calculated from menstrual dates and adjusted using an early ultrasound.

Pregnancy can begin when sperm fertilizes an egg. The fertilized egg divides into more cells as it travels toward the uterus. It then attaches to the uterine lining. This attachment is called implantation.

Cells around the developing pregnancy begin forming the placenta. The placenta is an organ that exchanges oxygen, nutrients, and waste products between the pregnant person’s blood and the fetus. Their blood supplies usually do not mix directly.

The umbilical cord connects the fetus to the placenta. The fetus develops inside the amniotic sac, which contains fluid that provides space and cushioning.

Hormones support these changes. One is human chorionic gonadotropin, usually shortened to hCG. Urine and blood pregnancy tests detect hCG. A urine test may be negative if it is taken too early or not used as directed.

Ultrasound uses sound waves to create images. It can help confirm where a pregnancy is located, estimate its stage, assess development, and identify more than one fetus. A very early ultrasound may not yet show enough to give a clear answer, so another test or scan may sometimes be needed.

Pregnancy affects circulation, breathing, digestion, kidney function, metabolism, and the muscles and joints. These changes help support the placenta and fetus, but they can also affect medical tests and treatment decisions.

Pregnancy changes the balance of benefits and risks for some medicines, vaccines, tests, and procedures. This does not mean that all medicines or medical care are unsafe. Leaving a health condition untreated can also cause harm.

Tell healthcare professionals about a pregnancy, or the possibility of one, before starting a new medicine or having a procedure. Do not stop a prescribed medicine suddenly unless a clinician advises you to do so.

Regular prenatal care checks the health of the pregnant person and the developing fetus. Care may include blood pressure measurement, blood and urine tests, ultrasound, screening for infections or genetic conditions, and discussion of mental health and social support. Which tests are offered depends on the stage of pregnancy, medical history, and local healthcare guidance.

Food safety also matters because pregnancy changes the immune response. Some foodborne infections can have more serious effects during pregnancy. Alcohol, tobacco smoke, and recreational drugs can also affect pregnancy and fetal development.

Most concerns described here are conditions that can affect a pregnancy. They are not “symptoms of pregnancy,” and this list cannot show what is happening in an individual case.

Miscarriage is the loss of a pregnancy before the stage at which a fetus could survive outside the uterus. Ectopic pregnancy occurs when a fertilized egg implants outside the uterus, most often in a fallopian tube. An ectopic pregnancy cannot develop normally and can cause dangerous internal bleeding.

Gestational diabetes is high blood sugar first identified during pregnancy. Gestational hypertension is high blood pressure that begins during pregnancy. Pre-eclampsia is a pregnancy-related condition involving high blood pressure and signs that organs, such as the kidneys or liver, may be affected.

Placental problems include the placenta covering the cervix or separating from the uterine wall too early. Other possible concerns include infection, poor fetal growth, fetal development differences, and labour that begins too early.

Seek emergency help now for:

• Heavy vaginal bleeding, fainting, or severe weakness
• Severe or worsening abdominal or pelvic pain
• Chest pain, severe trouble breathing, or coughing blood
• A seizure, loss of consciousness, or sudden confusion
• Thoughts of harming yourself or someone else

Contact a maternity service or other urgent healthcare service promptly for vaginal bleeding, fluid leaking from the vagina, fever, persistent vomiting with difficulty keeping fluids down, severe headache, vision changes, painful urination, or contractions before the expected time of labour. Once fetal movement has become regular, a clear reduction or change also needs prompt assessment.

Routine questions about tests, nutrition, medicines, work, travel, or expected body changes can usually be discussed at a scheduled prenatal appointment.

If a menstrual period is late or pregnancy is otherwise possible, a home urine test can provide useful information. Follow the package instructions. If the result is negative but pregnancy remains possible, repeating the test later or arranging a clinical test may clarify the result.

If a test is positive, contact a prenatal care service. Early contact allows time to review health conditions, medicines, previous pregnancies, and available screening.

Useful actions include:

• Record the first day of the last menstrual period, if known
• Keep a current list of prescriptions, supplements, and non-prescription medicines
• Ask whether any medicines need review rather than stopping them yourself
• Ask which prenatal vitamin and folic acid amount are appropriate
• Attend offered appointments, tests, and ultrasound scans
• Avoid alcohol, smoking, vaping, and recreational drug use
• Ask for support if stopping alcohol, nicotine, or drugs is difficult
• Follow local advice about food safety and recommended vaccines
• Keep contact details for routine, urgent, and emergency maternity care

There is no single test that can guarantee how a pregnancy will develop. Screening tests estimate the chance of certain conditions. Diagnostic tests aim to determine whether a specific condition is present. Before agreeing to a test, you can ask what it checks, how accurate it is, whether it has risks, and what the results could mean.

Is a positive home test a diagnosis?

A correctly used positive home test usually means hCG has been detected. A healthcare professional may confirm the pregnancy, estimate its stage, and check its location when medically appropriate. Fertility medicines containing hCG and a few medical situations can affect results.

Why can pregnancy dates change after an ultrasound?

Menstrual dating assumes a particular cycle and ovulation pattern. An early ultrasound measures the developing pregnancy and may provide a better estimate when dates are uncertain. Later scans are less useful for changing the original due date because fetal size naturally differs.

Are medicines always unsafe during pregnancy?

No. Some medicines are considered appropriate, some require extra discussion or monitoring, and others may need to be avoided. The answer depends on the medicine, dose, timing, reason for treatment, and available alternatives. Ask a pharmacist or pregnancy care clinician to review the complete list.

Can normal activities continue?

Many people can continue work, travel, exercise, and sexual activity during an uncomplicated pregnancy. Adjustments may be needed because of a medical condition, pregnancy complication, type of activity, or stage of pregnancy. Ask about any activity involving high-impact injury risk, heavy exposure to chemicals or infections, or limited access to medical care.

Who provides pregnancy care?

Care may be provided by a midwife, family doctor, obstetrician, maternal-fetal medicine specialist, or a team. The available options depend on health needs and the local healthcare system.