1st Trimester of Pregnancy – Week 1 to 13 – All You Need to Know

Fetal development begins soon after conception. Keep in mind that all the measurements below are approximate. Let us find out together how your baby grows and develops during the first trimester.

Week 1 – Getting ready

                Oops! We know by now you are not yet pregnant. To calculate your estimated due date, the first day of your menstruation period is very important to help your healthcare provider to calculate your estimated due date. From here, we will count ahead 40 weeks.

Week 2 – Fertilization occurred

The sperm and eggs unite in one of your fallopian tubes. Soon after fertilization, the zygote travels down the fallopian tube towards your womb.


Week 3 – Implantation

A microscopic ball of rapidly multiplying cells called Blastocyst start to attach into the lining of your womb. At this point, 15 to 25 % of women experience light bleeding called implantation bleeding.


Week 4 – Embryo formation

The size of your baby is of a poppy seed. Your ball of cells transforms to an official embryo.

The level of HCG hormone quickly increases. The embryo is now made up of three layers. If you do a home pregnancy test, you are highly likely to get a positive result.


Week 5 – Tiny tadpole

The size of your baby is of a sesame seed. The growth is rapid this week. The embryo is made up of three layers:

  • Ectoderm (outer layer) – Skin, central and peripheral nervous system, eyes and inner ears.
  • Middle Layer (Mesoderm) – Bones, ligaments, kidney, muscles of reproductive system.
  • Inner Layer (Endoderm) – Lungs, intestines, early urinary system, thyroid, liver, and pancreas.

The heart and other organs start to form. Your baby’s heart starts to beat. The baby brain and spinal cord will develop from the neural tube. The necessary structure for the formation of eyes and ear develops. Small buds appear that will soon become arms.


Week 6 – Formation of the head

Your baby is the size of a lentil. The heart is beating twice as fast as the mother’s heart. The eyes, nose, mouth, and ears start to form and show as dark spots. A small pouch on each side of the head marks the ears’ development. The lower limb buds appear to become legs after, and the arm buds take on the shape of paddles.


Week 7 – Eyes, digestive system and brain development

In this week, your baby is the size of a blueberry.  The eyes continue to develop and the necessary parts for the sight – the cornea, iris, lens, and retina – start forming. They continue developing till few weeks later.

Your baby’s stomach and the tube that moves food from your baby’s mouth to the stomach called esophagus start to form. The pancreas and the liver are developing this week too.

Amazingly, your baby’s brain gains an average of 250,000 cells per minute through the pregnancy. Now, the neural tube closes at both ends and becomes your baby’s spinal column and brain that is on the top. Your baby’s brain is made up of the following three areas:

  • Forebrain
  • Midbrain
  • Hindbrain

This phase is very important for their brain development which can be affected by your internal and external feelings and actions. Loving and connecting with your baby should start from pregnancy.


Week 8 – Baby movements’ week

You are on your week 8 now! Your baby is the size of a kidney bean. He is moving now by making spontaneous twitches and stretches that you won’t feel or notice.

We at AL Zahra Hospital are pleased to register you with us for the antenatal care.

Some highlights of week 8:

  • Baby’s fingers and toes appear
  • Nerves, bones, and muscles develop inside the limbs
  • Respiratory system starts to form


Week 9 – Basic anatomy development

Your baby is the size of a grape. The embryonic tail disappears and starts gaining weight fast.

Your body is growing two miracles inside, a complete baby and another organ called the placenta. Your baby’s body has all the essential body parts:

  • Baby’s elbow bends
  • Longer toes and fingers
  • Visible umbilical cord
  • Head becomes rounder.
  • Tiny earlobes form
  • The four chambers of heart form
  • Tiny tooth buds develop that will transform to baby teeth.


The placenta

The placenta is an organ that develops in your uterus during pregnancy. The placenta attaches to the wall of your womb and connects to the baby’s umbilical cord that arises from it. It is responsible to provide oxygen and nutrients to your growing baby and removes waste products from your baby’s blood.


Tips to consider:

  • Bonding with your baby
  • Connecting with your partner by encouraging them to be a part of your pregnancy
  • Walking is the safest activity unless you have been restricted by your doctor from some activities


Week 10 – Hearing your baby’s heartbeat

Your baby is the size of a kumquat.

The main parts of the eye that enable your baby’s vision are fully formed (the cornea, iris, pupil, and the retina). Your baby’s eyes are covered by the eyelids, and they will stay closed till 27 weeks.

Your baby’s forehead temporarily bulges with their brain development and stays very high on the head.

Buds for future teeth appear. Few babies might be born with one or two teeth. Normally, the teeth sprout out at 6 to 10 months old or even longer.

Week 11 – When you will feel kicks

Your baby’s size is of a fig. This is when you start thinking of announcing your pregnancy to the family and friends.


Highlights of week 11:

  • Genitals develop: Baby’s external genitalia will start developing into a penis and a scrotum in boys or clitoris and labia in girls. Differences are not easily seen at this stage.
  • Face becomes broad.
  • Fingers and toes are more distinct now and nails form.
  • Baby’s face is more developed.
  • Intestines are in the abdomen.
  • Some vital organs start working: The liver makes red blood cells, the kidneys make urine, and the pancreas starts making insulin. The four chambers of the heart are fully formed, and your baby’s heart is beating.

Your healthcare provider may auscultate the fetal heart rate by a Sonicaid.

Be sure to exercise safely, get enough rest, a healthy lifestyle, and healthy diet.


Week 12 – Reflexes week

Your baby is the size of a lime.

This week is the reflexes development week. Your baby can make small movements such as opening and closing their hands and curling their toes.

The abdominal wall will close, and their intestines make their way inside the abdomen.

It is time to do the nuchal translucency test and the NIPT blood test to screen for Down’s syndrome. This ultrasound scan is done between 11 and 14 weeks. Your doctor might have done already an ultrasound scan by now if you are at high-risk pregnancy to rule out miscarriages or ectopic pregnancy.


Week 13

Your baby is the size of a peapod.

Your baby begins to excrete urine in its surroundings, swallows the amniotic fluid and recycles the full amount every few hours.

Prints are forming on your baby’s tiny fingertips. Bones are beginning to harden in your baby’s skeleton especially in the skull and long bones.

For you mommy, you might notice that your morning sickness and fatigue have subsided. Your breasts start to harden making colostrum which is the first form of milk rich in nutrients that feeds your newborn baby for a few days after birth.

You might experience some cramping like pain. This is common. Call your doctor if your pain is constant, frequent and getting stronger after several minutes of rest.

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