A full-term pregnancy has 3 trimesters and lasts around 40 weeks — starting from the first twenty-four hours of the last menstrual catamenia. In each trimester, the fetus meets specific developmental milestones.

While twoscore weeks is the usual fourth dimension frame, a full-term baby tin can exist built-in as early as 37 weeks and as late as 42 weeks.

The Office on Women's Wellness defines the three trimesters as follows, though the timing can vary:

  • first trimester: ane–12 weeks
  • second trimester: 13–28 weeks
  • third trimester: 29–xl weeks

Some people also talk nearly a quaternary trimester, which is the 3-month transitional flow afterward delivery.

Read on for more information about what to expect during each pregnancy trimester.

Pregnancy trimester infographic

Image credit: Stephen Kelly, 2018

The first trimester is the first 12 weeks of the pregnancy, and information technology is a crucial time for fetal evolution.

The fetus

At conception, the egg and sperm combine to form a zygote, which implants in the wall of the uterus. The zygote becomes an embryo as its cells divide and abound.

By the end of the starting time 12 weeks:

  • All the torso's major organs and structures take begun to develop.
  • The centre is beating regularly.
  • Fingers and toes have formed.
  • The fetus is around 3 inches (in) long and weighs almost 1 ounce.
  • The fretfulness and muscles work together, and the fetus can make a fist.
  • The eyelids have formed and will remain closed until around week 28, to protect the eyes.

The pregnant person

A person also experiences many changes during their kickoff trimester of pregnancy.

These include:

  • fatigue
  • tender, swollen breasts
  • mood changes
  • cravings for certain foods
  • headaches
  • indigestion
  • a demand to urinate more than frequently
  • weight changes
  • constipation
  • nausea, sometimes with airsickness, known as morning sickness

Morning sickness tin can final throughout the outset trimester and sometimes beyond. Despite its name, information technology does non occur but in the morning.

Weeks 14–27 are the second trimester. The fetus goes through many changes during this fourth dimension, growing to be around i foot long and weighing one.five pounds.

The fetus

Past the end of the 2d trimester, the following will have happened:

  • Meconium, the starting time bowel move, has developed in the intestines.
  • The fetus can see, hear, make a sucking motion, and scratch itself.
  • Skin, hair, and nails accept formed.
  • The lungs take formed but practice not all the same piece of work.
  • The fetus is sleeping and waking regularly.
  • A male's testicles will have moved to the scrotum, and a female person's eggs will accept formed in the ovaries.
  • Taste buds have formed.
  • Bone marrow is making blood cells.
  • Lanugo, which is fine pilus, covers the body.

The significant person

Many people feel more comfortable during the 2d trimester of pregnancy. Morning time sickness and fatigue frequently reduce or disappear.

Meanwhile, new changes take place:

  • The abdomen expands as the fetus grows.
  • Stretch marks may announced on the abdomen, thighs, breasts, and buttocks.
  • The areola, the skin around the nipples, becomes darker.
  • The skin on the face and may darken in patches.
  • The ankles, fingers, and face up may swell.
  • Itching may occur. If information technology happens with airsickness or yellowing of the peel or whites of the eyes, known equally jaundice, seek medical communication.

It becomes possible to feel the baby'due south movements every bit this trimester progresses.

The third trimester lasts from calendar week 29 until delivery, which is usually around week xl.

The fetus

About organs and torso systems have formed past now, and they will continue to abound and mature.

During this trimester:

  • The bones are hardening.
  • Movements become more noticeable.
  • The eyes are open and can sense low-cal.
  • Lung germination becomes complete.
  • Lanugo falls abroad, and a waxy coating, called vernix, develops.

Toward delivery, the fetus drops lower in the person's belly and usually turns head-down.

The pregnant person

The growth of the fetus can cause new discomfort at this time.

A person might likewise experience:

  • heartburn
  • shortness of breath
  • swelling in the ankles, face, and fingers
  • insomnia
  • mood changes
  • leakage of milk from the breasts
  • other breast and nipple changes
  • frequent urination
  • hemorrhoids
  • Braxton-Hicks contractions, which do not indicate labor
  • real contractions, which indicate labor

It is also normal to feel feet about the commitment and parenthood toward the end of a pregnancy.

The 3 months after commitment play a key role in the wellness of the person and their babe. Some people phone call this transitional period a fourth trimester.

While this can be an exciting time, the range of hormonal and environmental changes can pose challenges.

These challenges might involve:

  • recovering after delivery, especially if there are stitches
  • dealing with lochia, a belch of blood and tissue, which may continue for several weeks
  • cramping, which may feel like menstrual cramping, especially during breastfeeding
  • adjusting to a new office of parenthood
  • learning new skills
  • having sore breasts and other difficulties related to breastfeeding
  • having fatigue, due to a loss of sleep and other factors
  • in some cases, experiencing postpartum low

Some tips for managing include:

  • limiting visitors, if this helps
  • asking others for help
  • reducing housekeeping duties
  • resting when the baby does
  • eating regularly, as far as possible
  • raising any concerns about the baby, breastfeeding, or personal health
  • attending all followup appointments

Anyone who experiences a persistent low mood, feelings of guilt or inadequacy, or thoughts of harming themselves or the baby should seek firsthand medical intendance and guidance. These can exist signs of postpartum low.

Pregnancy, childbirth, and the starting time few months with a newborn are dissimilar whatever other time in life. They are total of new experiences, great uncertainty, upheavals, and many new emotions.

Getting regular prenatal care is vital during each trimester. A doctor can help ensure that the fetus is meeting their developmental milestones and that the meaning person is in adept health. They can also provide guidance and resources for support.