A calendar pregnancy is a gestation and birth that is right on schedule according to nature's plan. In a calendar pregnancy the baby is born 42 weeks after the day of conception. White it may seem that a calendar pregnancy is unusual the fact is that errors or off-schedule pregnancies are generally because of the mother's inability to correctly pin down the date of conception.

Here are some of the key points in a calendar pregnancy. Week one is actually the week in which mom is not really sure she is pregnant. To be on the safe side a woman should assume she is with child unless she learns otherwise - refraining from birth control, alcohol and tobacco.

Week two is when the mother to be's uterine lining is getting thicker and ovulation is occurring.

Week three is really the start of mom's little one. Her ovulation has connected with sperm and she may have a slight big of bleeding due to implantation. Her body releases something called Early Pregnancy Factor (EPF) a protein that acts as an immunosuppressant so that her body will not treat the new baby as an invader. The baby begins its trip down mom's fallopian tube and about one week later becomes embedded in the uterus. At this point the tiny little baby is called a blastocyst, and measures at the most .2 millimeters.

The baby officially becomes a fetus at week ten of the calendar pregnancy, when the mother's waistline starts to disappear and the baby is up to 35 mm in length with toes, genitalia, ears, and upper lip. By week 18 the mother will be advancing enough to find sleeping difficult and the baby will have pads on its toes and fingers.

Week 24 is an important one in a woman's calendar pregnancy. The top of the mom's uterus, called the fundus, is now above the navel, and she can feel the baby moving and even tell when the wee one is awake or asleep. This is a time when premature labor can become a concern especially in the summer when the mom can become dehydrates. Early signs of premature labor are cramping more than five times each hours, bright red vaginal blood, puffy or swollen hands or face, painful urination, sharp stomach pain, vomiting, sudden vaginal gushing of water, a backache that is low and dull and intense pressure in the pelvic area.

By this time the baby is almost all formed and is forming body fat to keep warm. A baby that is born in the 24th week has a slight chance of surviving if given special intensive care. Lung development is the primary problem with premature babies. At 24 weeks in a calendar pregnancy a baby weighs less than 1 ½ pounds.

By week 36 the baby has moved into a head down position. He or she continues to grow and to move down into the mother's pelvis. The result for the mom is that she can now breathe more easily because of the baby's having dropped but the extra weight on her bladder causes her to urinate more often.