Pregnancy: Weeks One to 40, Emotional & Physical Changes

A Detailed Look at All the Changes That Take Place

In pregnancy, a fertilized ovum implants in the uterus and develops into an embryo and fetus before being born. The pregnant person will experience changes throughout pregnancy, beginning with missing a menstrual period.

Physical changes and symptoms during pregnancy include menstrual period absence, morning sickness, breast changes, weight gain, change in body shape, feeling fetal movement, and more.

Pregnancy is divided into three trimesters. The first trimester lasts from week one to week 12. The second lasts from week 13 to week 26, and the third lasts from week 27 to the end of pregnancy.

Your healthcare provider will help you determine your due date, the date when you are most likely considered full-term and ready to give birth. The due date is calculated 40 weeks after the first day of your last period.

This article will provide an overview of pregnancy, focusing on how it feels and what to expect.

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Knowing exactly when your pregnancy starts is not as straightforward as you’d imagine. Many people refer to “how many weeks they are” to keep track of their pregnancy. This is based on the fetus’s gestational age. Gestational age starts on the first day of your last period before conception.

To understand the beginning of pregnancy, it’s important to start with the menstrual cycle. The average length of a menstrual cycle is 28 days but can range from 24 to 38 days. A person with a 28-day menstrual cycle usually ovulates around day 14.

The first two weeks of your pregnancy include your menstrual period and fertilization. About two weeks into your menstrual cycle, you will experience ovulation (the release of an egg from the ovary). The timing can vary depending on the length of your menstrual cycle. The average day to ovulate is day 14.

During ovulation, your ovaries release their most mature egg, which travels down the fallopian tube. This is where the egg meets the sperm and is fertilized (if pregnancy occurs).

During weeks three and four of your pregnancy, the fertilized egg travels to the uterus and begins dividing into more cells. It usually reaches the uterus about three to four days after fertilization.

Once this cluster of cells implants into the uterine wall (known as implantation), you are officially pregnant. Implantation occurs about six days after fertilization and takes three to four days to complete.

Most people do not know that they are pregnant in these early weeks because there are usually no signs. The first sign of pregnancy is often a missed menstrual period. Once you notice that you did not get your period, it’s time to take a pregnancy test.

A pregnancy test measures the amount of human chorionic gonadotropin (hCG), a hormone, in your urine to detect pregnancy. Your body starts producing hCG after implantation, and the level doubles every 48 hours in the first few weeks of pregnancy.

If you take a test too early, your body may not have enough hCG to produce a positive result. When used correctly, home pregnancy tests are 99% accurate.

Prenatal care is the medical care that you receive from the time you find out you are pregnant until the pregnancy ends. Prenatal care includes the healthcare appointments and medical tests you will undergo throughout pregnancy. Participating in prenatal care is an essential way to take care of the health of both you and your baby.

The first trimester is a time of rapid change for both you and the embryo. You may not look very different on the outside, but your body is hard at work. The first trimester includes conception, implantation, and embryo development.

The early pregnancy symptoms you may experience during the first trimester include:

During the second trimester, your baby officially becomes known as a fetus rather than an embryo. The second trimester is the time when many people begin to “show” and develop a pregnant belly.

Many pregnant people begin feeling fetal movement around week 20. This often feels like light flutters (as opposed to strong kicks). By the 24th week of pregnancy, your fetus is beginning to sleep and wake at regular intervals. Loud noises may even wake them up.

Most pregnant people have an ultrasound exam between 18 and 20 weeks of pregnancy. During this exam, an ultrasound tech or sonographer will use the ultrasound machine to visualize your fetus and check for any anatomic anomalies.

The second trimester is often a time of improved symptoms. You may notice that you suddenly feel less tired and nauseous. It’s common for new symptoms to begin as well.

Possible second-trimester symptoms include:

As you enter your third trimester, your fetus’s body is getting ready for life outside the womb. Their bones are soft and almost fully formed by week 32. In the third trimester, your fetus begins gaining about one-half pound each week and moves into a head-down position.

Babies born between 37 and 38 weeks are considered early term. Babies born at 39 or 40 weeks are full term, and babies born at 41 weeks are late term. Babies born after 42 weeks are considered post-term.

In the third trimester, many of your symptoms continue. These include fatigue, shortness of breath, and Braxton-Hicks contractions. New symptoms you may notice include:

Heartburn and constipation may improve once your baby “drops”—moves into the lower part of the pelvis—near the end of the third trimester.

If you have been experiencing infertility, you’re not alone. In the United States, about 10% of females between the ages of 15 and 44 experience difficulty getting pregnant. Infertility is defined as not becoming pregnant after trying for one year. (The terms for sex or gender from the cited source are used.)

There are several factors that affect your fertility, including stress, weight, diet, smoking, alcohol use, health conditions, and medications. If you are experiencing infertility, talk with a healthcare provider. If you are over 35, talk with a healthcare provider if you have been trying to become pregnant for more than six months.

Taking care of your health during your pregnancy can quickly begin to feel like a full-time job. There is so much to remember each day, and the care can start to feel overwhelming.

The most important step you can take to care for your pregnant body and baby is to connect with a healthcare provider. Receiving regular prenatal care reduces the risk of pregnancy complications.

Goals for your prenatal care may include:

There are also actions that you can take on your own. Lifestyle goals during pregnancy include:

It would be impossible to discuss prenatal health goals without addressing the inequities that exist within the healthcare setting. In the United States, Black pregnant people are 3 times more likely to die from a pregnancy-related cause than White pregnant people. About 80% of pregnancy-related deaths in the United States are preventable.

The factors involved in the health disparities affecting Black pregnant people (and those of other racial and ethnic groups) vs. non-Hispanic Whites include:

Pregnancy is an overwhelming time full of physical and emotional changes. You’re likely feeling a range of emotions, and that is normal. Because of the biological changes that occur during pregnancy, you also will experience many physical symptoms, and they will likely change as your pregnancy progresses.

Once you learn that you are pregnant, it is crucial to find a healthcare provider such as an ob-gyn or certified nurse midwife. Getting regular prenatal care is one of the most important ways you can take care of yourself and your baby during pregnancy.

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By Carrie Madormo, RN, MPHCarrie Madormo, RN, MPH, is a health writer with over a decade of experience working as a registered nurse. She has practiced in a variety of settings including pediatrics, oncology, chronic pain, and public health.