Pregnancy: The first month

PDF download is not available for Arabic and Urdu languages at this time. Please use the browser print function instead.

Learn about the changes that occur during the first month of pregnancy. Physical and mental changes, medical concerns, and depression are discussed.

Key points

  • The first month of pregnancy begins in the third week after your last menstrual period.
  • During weeks five and six, you may start to realize you are pregnant and experience increases in physical symptoms.
  • Concerns in the first month of pregnancy include ectopic pregnancy, miscarriage and teratogens.
  • It is normal to experience mood swings in response to the changes you are going through in your pregnancy.

The first month of pregnancy begins in the third week after your last menstrual period. The first few weeks of pregnancy bring with them a unique set of physical and emotional changes. There are also several concerns during the first month including ectopic pregnancy, higher risk of miscarriage, and teratogens.

Physical changes in the first month of pregnancy

During week three, the egg cell is fertilized by a sperm cell in the fallopian tube. The fertilized egg cell travels through the fallopian tube to implant in the uterus. During implantation, you may have a tiny bit of bleeding, called implantation bleeding. Also this week, a hormone called early pregnancy factor (EPF) is released. EPF prevents your body from rejecting the baby as an invader.

Starting in week four, you will experience many physical symptoms that will last throughout the first trimester of pregnancy. A hormone called human chorionic gonadotropin (hCG) is released in your body during the first 12 weeks of pregnancy, and this hormone is associated with symptoms such as mood swings, nausea and vomiting. Other symptoms of pregnancy include fatigue, frequent urination, tender or swollen breasts, and a strange, metallic taste in your mouth. You may also start to experience cravings or aversions to certain types of food.

In weeks five and six, you may start to realize that you are pregnant. Your period may be late. Your fatigue and other symptoms will continue. Your nausea may increase due to rising hormone levels. Nausea in pregnancy tends to get worse on an empty stomach, so try to keep some plain biscuits or crackers on hand and eat frequent, small, high-carbohydrate meals throughout the day. Although nausea in pregnancy is typically referred to as morning sickness, it can strike at any time of the day.

Your urge to urinate will increase as your expanding uterus presses on your bladder. Your breasts will continue to feel tender, swollen, and heavy. Your nipples will become darker and the veins in your breasts more noticeable. You may develop headaches, caused by the increasing levels of hormones in your system.

Do not fret if you do not develop all of the so-called symptoms of pregnancy! For example, some women sail through their first trimester without any nausea at all.

Concerns in the first month of pregnancy

Ectopic pregnancy

One of the main concerns during the early part of this month is the risk of an ectopic pregnancy. During week three, if the fertilized egg cell implants itself outside the uterus, most often in the fallopian tube, the growing set of cells will eventually rupture the tube, causing significant internal bleeding and severe pain in the woman's abdomen. If an ectopic pregnancy is discovered early enough, sometimes a drug can be given to end the pregnancy. Otherwise, urgent surgery will be required to bring the pregnancy to an end; rarely, the fallopian tube may need to be removed.


The risk of miscarriage is highest in the first trimester. During these first few months, there are many things that can cause a miscarriage. By far the most common reason for miscarriage is a problem with the chromosomes in the embryo. This could be nature’s way of ending a pregnancy when the child would be unable to survive. Other reasons for miscarriage include hormonal problems and abnormalities of the uterus.


Teratogens are infections or substances such as alcohol, drugs, certain medications and some chemicals, which can cause birth defects. The first trimester is an extremely critical time for your baby’s development. All of the major organ systems and structures form in these three months. Therefore, you should make sure to stay away from teratogens during this time and throughout your pregnancy.

Emotional changes and depression in the first trimester of pregnancy

Usually, the first trimester of pregnancy is a time of great joy for the expectant mother. You will no doubt be excited and perhaps relieved when you discover you are pregnant. However, you may also have mixed feelings about your pregnancy. Unpleasant physical symptoms such as nausea or vomiting may make you feel resentful. You may feel frightened because of a bad experience with a previous pregnancy. You may be worried about the alcohol you drank before you knew you were pregnant, or whether you will be able to stick with your nutrition plan. You could be concerned about losing the baby. You might worry about whether you will be able to take care of a baby, or whether you can afford a child.

Self-esteem issues also come into play at this time. As your clothes become tighter, you might start to feel less attractive. If your professional activities are important to your self-esteem, you may feel isolated from peers and unable to meet the expectations of your superiors.

It is normal to have mood swings in response to all the changes you are going through in your pregnancy. These mood swings can range from elation to being upset, angry, or depressed. It is important to keep in mind that these feelings are normal during pregnancy. If you are getting into petty arguments with your spouse because of your mood swings, try to talk things over with them, to make sure the problems don’t escalate.

Some women may experience a depression that is so pronounced and continuous that it disrupts their normal functioning. This is called major depression, and it affects 4% to 12% of women during pregnancy. The incidence of major depression during pregnancy is not as high as during the postpartum period (12% to 28%). However, if you have depression during pregnancy, you are more likely to have postpartum depression​. If you have any of the following symptoms of depression, check with your doctor:

  • feeling out of control
  • unpredictable tearfulness and spontaneous crying
  • feelings of sadness, melancholy, weary anger, or general despair
  • sleep disturbances
  • a total loss of sexual desire

Overall, though, most women simply have an intense and romantic sense of excitement in the first trimester of pregnancy. There is a feeling of joy, and of being more special than anyone else in the world.

How your baby is developing

Last updated: September 11th 2009