What are the three trimesters of pregnancy?

The three trimesters of pregnancy are the First Trimester, Second Trimester and the Third Trimester. The fetus goes through different stages of development during each trimester. It is calculated from the last menstrual to the birth of the baby, approximately 40 weeks.

First Trimester

This stage covers the first 12 weeks of the pregnancy. Conception takes place in the fallopian tube when a sperm penetrates the ovum and donates its genetic material or DNA. During this stage the two cells called gametes form a single cell called zygote. The zygote then travels from the fallopian tube to the uterus while devolping into a multi-cellular blastocyst. Once in the uterus, the blastocyst attaches itself to the uterine lining also refered to as the endometrial cell layer. After the implantation is complete the embryo starts growing rapidly and is approximately 3 inches in length by the end of 12 weeks. The head of the embryo is comparatively large and has a clearly visible spine along with developing teeth buds, vital organs, eyes, fingers and toes. Morning sickness occurs during this stage in most women along with several emotional and physiological changes due to changs in hormonal levels. The First Trimester is critical as most miscarriages occur during this stage for various reasons.

Second Trimester

This stage covers week 13 to week 25 of the pregnancy. The fetus may be able to hear the mothers voice as the ears develop in this stage. The bones start hardening and the fine hair starts growing all over the fetus. Also this is the stage where fetal movement (quickening) can be felt for the first time. The sleeping patterns of the fetus also become distinct. The morning sickness symptoms reduce considerably and most women feel energised and start putting on weight. The fetus also develops reproductive organs enabling sex identification at this stage.  

Third Trimester

This stage covers week 26 of the pregnancy until birth around week 40. During this stage the fetus grows the most and gains weight rapidly. The belly shape of the woman will also change rapidly and as it drops downwards from the upright position during the second trimester. The fetus turns to a downward position  while preparing for the birth. There is frequent fetal movement which can be felt by the woman. This can also cause a lot of discomfort or pain due to the pressure on the spine or ribs and weak bladder control. The baby can survive even if it is born prematurely during this stage.

Submitted by P T on January 14, 2010 at 08:28

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