By Neus Ferrando Gilabert BSc, MSc (embryologist).
Last Update: 10/27/2014

Many people will be surprised when hearing 10 months, since it always has been said that pregnancy lasts 9 months. Truth be told, pregnancies last between 38 and 42 weeks. Pregnancies usually last 40 weeks. Doctors don’t count pregnancy in months but in weeks.

We must also take into account that not every month has exactly 4 weeks. If we divide 365 days into weeks, the result will be approximately 52, which divided into months, is about 4.34 weeks per month. That’s why some months have almost five weeks. That’s the reason why we are talking about a ten months pregnancy, even though it’s most appropriate to say week 37, 38, 39 and 40.

The different sections of this article have been assembled into the following table of contents.

General changes by week

During this month the child is getting ready for birth. His organs function on their own and even the lungs have developed completely. Your uterus is responsible for making sure that the child is born and will exert the right pressure to ensure that birth takes place.

The child grows from 48 cm at the beginning of the 10th month of pregnancy until achieving approximately 51 cm. The weight increases from 1980 grams until achieving 2730 grams approximately on average.

Week thirty-seven of pregnancy

The child may begin to try to breathe, rehearsing some respiratory movements. He doesn’t have air in the lungs, but he is getting ready for the moment of birth. He may swallow amniotic fluid and have hiccups that you may feel.

The lanugo covering his body has disappeared except for the shoulders and the upper part of the arms.

Week thirty-eight of pregnancy

The nails grow beyond his fingers and he can scratch himself and even hurt himself.

He may move less, but don’t worry, due to his size he can no longer move freely inside the womb. It’s also quite common to feel pressure in the vagina; the baby exerts pressure on the pelvis. He is getting ready for birth.

Week thirty-nine of pregnancy

During week 39 your cervix is getting ready for birth. You may feel heavy and experience quite strong Braxton Hicks contractions. There might even be some false alarms, you may think that the baby is going to be born and then come home empty-handed from the hospital.

The amniotic fluid keeps renewing every 3 hours. The baby’s intestine is full of black greenish meconium, caused by secretions of the alimentary glands, bilirubin and biliverdin, lanugo and cells from the intestine wall. This will be the content of the first faeces after birth.

Week forty of pregnancy

If it hasn’t happened yet, birth is likely to take place during this week. It won’t be long until you can hold your baby, be patient.

Birth is not easy and don’t worry if you feel scared, you’ll get over it and once you see your baby’s face, you’ll forget all the suffering and pain.

However, sometimes it takes longer for the babies to be born. You may have to wait longer. If birth has not taken place during week 42, the doctors will have to induce it. A longer pregnancy can cause problems, both for the baby and the mother.

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Authors and contributors

 Neus Ferrando Gilabert
BSc, MSc
Bachelor's Degree in Biology from the University of Valencia (UV). Postgraduate Course in Biotechnology of Human Assisted Reproduction from the Miguel Hernández University of Elche (UMH). Experience managing Embryology and Andrology Labs at Centro Médico Manzanera (Logroño, Spain). More information
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