Pregnancy in Humans

 Introduction of Pregnancy 

It is the condition of carrying one or more embryos in the uterus. It is also called gestation. It refers to the period between fertilization of the egg, upto parturition. The average period of pregnancy in human lasts for 266 days from fertilization or 280 days (266+14) counted from LMC- Last Menstruation Cycle.  

1. First Trimester- (Period from fertilization to 12th week) 

• It is the time of most radical changes in mother and embryo. The embryo receives nutrients in the first 2-4 weeks directly from the endometrium. 

• By the end of eight weeks, The embryo is now called foetus and is about 3cm long. The arms, hands, fingers, feet, toes are formed and the foetus can open and close its mouth and fists. CNS is fully formed, working of excretory and circulatory systems begins. Movements of foetus begin but mother can not feel it.  

• Heart beat can be heard from 6th week. At the end of first trimester foetus is about 7-10 cm long. 

• In mother’s body progesterone level becomes high and menstrual cycle is suspended till the end of pregnancy. 

• The maternal part of placenta grows, the uterus becomes larger. In this period, the mother experiences ‘morning sickness’ (nausea, vomiting, mood swings, etc.) 

2. Second Trimester- (Period from 13th to 26th week) 

• It is the period of rapid growth of foetus. The foetus is very active and grows to about 30 cms. Development of brain begins.  

• Hormone levels stabilize, human chorionic gonadotropin (hCG) declines, the corpus luteum deteriorates (regresses) and the placenta completely takes over the production of progesterone which maintains the pregnancy.  

• Ultrasound (sonography) at 18-20 weeks shows baby’s growth and position. Baby’s movements can be easily felt by the mother. Head has hair, eyebrows and eyelashes appear, pinnae are distinct. The baby reaches half the size of a newborn.  

3. Third (final) Trimester- (Period from 27th week till the parturition).  

• The foetus grows to about 3-4 kg in weight and 50 cms in length. Eyes are open.  

• There is gain in body weight. As the foetus grows, the uterus expands around it, the mother’s abdominal organs become compressed and displaced, leading to frequent urination, digestive blockages and strain in the back muscles.  

• At the end of third trimester the foetus becomes fully developed and ready for parturition.