Congratulations on becoming pregnant! Follow your little one’s development month by month, from conception to labor, in this detailed guide to fetus development stages.

First trimester

The first trimester comprises the first 12 weeks from conception. During this phase of pregnancy, the fertilized egg will change from a cluster of cells to a fetus that starts to develop baby features.

Month 1 (weeks 1 through 4)

After an egg is fertilized, a water-tight sac will form around it, gradually filling with fluid. This is known as the amniotic sac, and it serves the role of cushioning the growing embryo. The placenta also develops during this period. This round, flat organ transfers nutrients from the mother’s bloodstream to the developing embryo and also transfers waste from the embryo.

By the end of week 4, the basic structures of the embryo will have begun to develop into separate sections that will form the head, abdomen, chest, and organs within them. Small buds on the surface will form into legs and arms.  

Month 2 (weeks 5 through 8)

During the second month, the embryo develops a tiny mouth, nose, and ears. The eyelids will also form but will stay shut until later in the pregnancy. Some of the significant organ development during this month includes:

• The lungs connecting to the throat with breathing tubes
• The heart (beating at about 105 beats per minute)
• The neural tube (spinal cord, brain, and other neural tissue of the central nervous system)
• The digestive tract
• The sensory organs

By the end of week 8, your little one will graduate from an embryo to a fetus.

Month 3 (weeks 9 through 12)

The hands, fingers, arms, feet, and toes are fully formed at this stage. The fetus will start opening and closing its mouth and fists. External ears will form and the fingernails and toenails will begin to form. 

By the end of month 3, the fetus will be fully formed. That means that all the limbs and organs are present and will continue to develop to allow for functionality. Although the reproductive organs will also have begun to develop, it’s still difficult to determine gender on ultrasound at this stage.

Second trimester

Many women consider the second trimester to be the best phase of pregnancy. By this time, morning sickness should be mostly gone and the discomfort associated with the first trimester has faded. One of the most exciting things about this trimester is that you can find out your baby’s gender.

Month 4 (weeks 13 through 16)

Your fetus can move his/her facial features, although any expressions are random. The nails, hair, eyebrows, and eyelashes are formed, and the teeth and bones become denser. The fetus can yawn, stretch, and even such his/her thumb.

The nervous system starts to function, and the reproductive organs and genitalia are fully developed, which means your doctor can see during an anatomy scan (an ultrasound that tracks physical development) if the fetus will be designated female or male at birth.

Month 5 (weeks 17 through 20)

You may have already started feeling your baby moving at around five months. As the fetus’s muscles continue to develop, you’ll notice that those flutters and kicks from their movements get progressively stronger, and you may soon pick up on patterns of more intensive activity, followed by quieter periods.

Hair will start to grow on the head, and soft fine hair known as lanugo will grow on the back, shoulders, and temples. The baby’s skin is covered with a whitish coating known as vernix caseosa that is believed to protect the fetal skin from long-term exposure to the amniotic fluid.

Month 6 (weeks 21 through 24)

By the sixth month of pregnancy, you’ll have probably gotten used to your baby’s somersaults and kicks, but you may also feel him/her move suddenly in response to loud sounds outside your belly. You may also notice jerking motions if your little one hiccups.

The skin of the fetus is reddish in color and wrinkled, and there are prominent veins on the translucent surface. This is the stage where the eyelids start to part and the eyes open.

Month 7 (weeks 25 through 28)

At this point of pregnancy, your little one’s hearing is fully developed. The fetus also develops reserves of fat, which means his/her skin gets smoother as he/she gains weight. Another notable thing during this month is that the fetus changes positions frequently and can respond to different stimuli, including light, sound, and pain. 

Third trimester

This is the last stage of pregnancy. Keep in mind that even though it’s believed that women are pregnant for nine months, you may actually be expectant for ten months. Typically, full-term pregnancy is 40 weeks, which means you can reach the ten-month mark. Some women even go past their due dates by a week or two (41 or 42 weeks). As you approach your due date, your healthcare provider will keep a close eye on you. If you go past the due date and fail to go into spontaneous labor, you may have to be induced.

Month 8 (weeks 29 through 32)

Your little one continues to grow and develop reserves of body fat. Kicks and flutters may intensify in this month. The brain is rapidly developing, and the fetus can hear and see. Most internal systems should be fully developed, but the lungs may still be underdeveloped.

Month 9 (weeks 33 through 36)

At month 9, the lungs are close to being fully developed. The fetus is able to respond to light, sounds, and touch, can blink, turn the head, close the eyes, and grasp firmly.

Month 10 (weeks 37 through 40)

This is the final month, which means you could go into labor at any given moment. Movements will reduce because there isn’t much space. The fetus may have changed his/her position to prepare for birth. Ideally, the head should face towards your birth canal.

Final thoughts

Your baby’s growth and development in your belly during pregnancy is delightful, but it can also be nerve-wracking because it’s unpredictable. It can be helpful to learn the fetal milestones your baby will achieve each month. Hopefully, this guide has helped you achieve that. Good luck!