निषेचन (फर्टिलाइजेशन) के ठीक बाद... Right after Fertilization…

Author : Dr. P. D. GUPTA

Former Director Grade Scientist, Centre for Cellular and Molecular Biology, Hyderabad, India


At the moment of fertilization, the baby’s genetic make-up is complete, including its sex. The gender of the baby depends on what sperm (X or Y carrying chromosome) fertilizes the egg at the moment. This stimulation changes endocrinology and physiology of the females body. Hereafter, the female’s body starts changing to meet the demands. Hormones play a central role in regulating fetal growth and development. New hormone is synthesized namely, Human chorionic gonadotropin (hCG);  hCG serves as one of the first signals provided by the embryo to the mother. Exactly at the time when the first step of the implantation process is initiated and the blastocyst adheres to the maternal endometrium, the embryonic tissue starts to actively secrete hCG. hCG is produced primarily by syncytiotrophoblastic cells (those cells which form placenta) of the placenta during pregnancy. The hormone stimulates the corpus luteum to produce progesterone to maintain the pregnancy. Smaller amounts of hCG are also produced in the pituitary gland, the liver, and the colon. Positive test for hCG confirms pregnancy.     

They act as maturational and nutritional signals in utero and control tissue development and differentiation according to the prevailing environmental conditions in the fetus. Hormones signal the body when to grow and when to stop growing.  These hormones travel to other cells and help control or coordinate many body processes, such as regulating mood, growth and development, tissue function, metabolism, as well as sexual function and reproductive processes. Estrogen and progesterone are the chief pregnancy hormones. A woman will produce more estrogen during one pregnancy than throughout her entire life when not pregnant. Progesterone made by  the corpus luteum makes the uterus  a highly vascularized bed for a fertilized egg.

The start of pregnancy is actually the first day of your last menstrual period. This is called the gestational age, or menstrual age. It’s about two weeks ahead of when conception actually occurs. Though it may seem strange, the date of the first day of your last period will be an important date when determining your baby’s due date. Your healthcare provider will ask you about this date and will use it to figure out how far along you are in your pregnancy.

In these early weeks, the embryo attaches to a tiny yolk sac. This sac provides nourishment to the embryo. A few weeks later, the placenta forms in full and takes over the transfer of nutrients to the embryo. Cells from the placenta grow deep into the wall of the womb.During the first trimester with one fetus, usually no extra calories are needed. In the second trimester, you will need an extra 340 calories per day, and in the third trimester, about 450 extra calories a day. To get the extra calories during the day, have healthy snacks on hand, such as nuts, yogurt, and fresh fruit.

When you're pregnant, you need more of certain nutrients — like protein, iron, folic acid, iodine, and choline. It's also important to get enough calcium, vitamin D, potassium, and fiber. Making smart food choices can help you have a healthy pregnancy and a healthy baby. Folic acid, iron, zinc, calcium, vitamin C, and vitamin D (in addition to energy and protein), are the main micronutrients for which the requirement physiologically increases during pregnancy and lactation.

Your baby's growing from 3 layers: the first layer becomes the nervous system and brain. the second layer will be the major organs, such as the digestive system and lungs. the third layer will be the heart, blood system, muscles and skeleton

The first organ system to develop during organogenesis is the cardiovascular system. The heart has established its four chambers by four weeks of development, whereas week six involves cardiac outflow separation and descent of the heart (and lungs) into the thorax.

Almost all organs are completely formed by about 10 weeks after fertilization (which equals 12 weeks of pregnancy). The exceptions are the brain and spinal cord, which continue to form and develop throughout pregnancy.

The brain and nerve cells require a constant supply of oxygen and will die within a few minutes, once you stop breathing. The next to go will be the heart, followed by the liver, then the kidneys and pancreas, which can last for about an hour. Skin, tendons, heart valves and corneas will still be alive after a day. (The author has his own study and views)