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Medical News Today: 5 weeks pregnant: your pregnancy week by week

You are now 5 weeks pregnant and have entered what is called the embryonic period of development; during this time your baby’s major organ systems and structures will develop.1

At this stage in development, the embryo’s cells differentiate or multiply and will begin to take on specific functions.1

This MNT Knowledge Center feature is part of a series of articles on pregnancy. It provides a summary of each stage of pregnancy, what to expect, and insights into how your baby is developing.

You will also see introductions at the end of some sections to any recent developments that have been covered by MNT‘s news stories. Also look out for links to information about related conditions.

Symptoms at 5 weeks pregnant

You will likely have missed your period and a pregnancy test should be taken.

You may also be noticing some early symptoms of pregnancy including mood swings, breast tenderness, exhaustion, waves of nausea and urinary frequency.2,3

fetus week 5
While all your baby’s organs are developing, the primitive placenta and umbilical cord are functioning to provide your baby with the nourishment and oxygen necessary for survival.

Your hormones

There are various hormones circulating throughout your body to maintain and support your pregnancy.

  • Estrogen: the hormone estrogen is produced to maintain your progesterone and hCG levels3
  • Progesterone: the hormone progesterone has many responsibilities. Not only is it responsible for maintaining placental function, but it is also responsible for inhibiting uterine contractions and stimulating breast tissue growth3
  • Human Chorionic Gonadotropin (hCG): the hormone hCG is also vital to the health of your pregnancy as it supports the primitive means of nourishment to your baby, the corpus luteum. At the end of the first trimester, the placenta will be fully functional. HCG is additionally responsible for maintain adequate levels of progesterone.3

Baby’s development at 5 weeks pregnant

Your baby is growing at a rapid pace with several cell types and organs starting to develop including the blood cells, kidney cells, nerve cells, brain, spinal cord, heart, and gastrointestinal tract.1

sesame seeds on a spoon
At 5 weeks pregnant, your baby is the size of a sesame seed.

Additionally, the neural tube responsible for forming the brain, spinal cord, nerves and backbone is developing from the ectoderm, which will also form the skin, hair, nails, mammary and sweat glands and tooth enamel.2

Your baby’s heart and circulatory system will form from the mesoderm, which will also form muscles, cartilage, bone and subcutaneous tissues.2 Your baby’s heart, which is now divided into two “tubes,” may be visible beating on an ultrasound.3

This time gives way to the development of the lungs, intestines, urinary system, thyroid, liver and pancreas from the endoderm.

While these organs are developing, the primitive placenta and umbilical cord are functioning and are providing your baby with the nourishment and oxygen necessary for survival.2

Your growing baby is vulnerable to the effects of various elements including the use of certain medications, illegal drugs, excessive alcohol use and infections (rubella, etc.). The effects of these elements can lead to birth defects.1

Baby’s size at 5 weeks pregnant

Your baby is now the size of a sesame seed and resembles more of a tadpole than a baby!2

Recent developments on pregnancy from MNT news

Pregnancy test: how early can you take a pregnancy test?

All pregnancy tests measure the amount of human chorionic gonadotrophin (HCG) – the pregnancy hormone. MNT explains how pregnancy tests work, when to take one, and their accuracy.

Antidepressants linked with risk of birth defects

In recent years, numerous studies have reported that there may be a link between maternal use of a class of antidepressants known as selective serotonin reuptake inhibitors and greater risk of birth defects. Now, a new study provides further evidence of this association.

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