Pregnancy begins the moment the egg and sperm join to form a fertilized egg. This typically happens approximately 14 days after the start of the last period, assuming the woman’s cycle is 28 days long. It usually takes approximately two weeks from conception to the earliest time a woman can find out if she is pregnant. However, thre are some signs that can occur as early as the moment of fertilization.
HCG
The moment the egg and the sperm unite, the release of a pregnancy hormone known as hCG begins. The amount of hCG present in a woman before fertilization is very small. According to a study published in "Fertility and Sterility” in 1982 by Dr. E. A. Lenton, approximately 5 milli-International Units per milliliter (mIU/ml) of hCG can be found in the blood around this time. Yet, the most sensitive beta hCG tests can detect even this tiny amount of hCG in the blood. It pays off to wait, however. The ammount of hCG in the blood rises rapidly until approximately 25mIU/ml can be detected. This usually happens nine days after conception, when the embryo connects itself to the walls of the uterus. At this time, most beta-hCG pregnancy tests can detect pregnancy.
Basal Temperature Stays High
According to GettingPregnant.com, around the time of ovulation, the basal temperature of the mother goes up by roughly 0.4 to 0.6 degrees Farenheit. This increase in temperature is caused by a hormone called progesterone. The basal temperature continues to stay up if the woman gets pregnant. On the contrary, if the egg is not fertilized, the woman’s temperature usually drops in about a day before the start of her period. Thus, higher basal temperature can be used as an early indication of pregnancy. It should be noted, however, that there are some individual variations in temperature changes, so this method is only reliable if a woman has been measuring her temperature daily during her entire cycle. Only then is it easy to detect the rapid increase in the temperature of her body and predict possible pregnancy.
Mood Swings
Mood swings are commonly reported during early pregnancy. They are most likely caused by the rapid increase in the levels of some hormones, such as progesterone and estrogen. For example, the levels of progesterone are approximately 20mg a day during a regular menstrual cycle. However, during pregnancy, these levels can be as high as 400mg per day. Moreover, during pregnancy, a woman can produce more estrogen in one day than a non-pregnant woman produces in three years, according to RnCeus.com. Because both of these hormone levels are strongly affected by pregnancy, they go up almost instantly following the start of pregnancy and can affect the mood a woman is in shortly afterwards.
Swollen, Tender Breasts
The same hormones, progesterone and estrogen, that can trigger mood swings can also cause the breasts of a pregnant woman to grow larger, and feel tender and soar. According to the Mayo Clinic, this may be one of the earliest visible signs of pregnancy in some women.
Slight Bleeding
Less than two weeks after ovulation, the fertilized egg reaches the uterus and connects itself to the walls of the uterus. This process is called implantation and can cause slight spotting or vaginal bleeding in some women. Many women mistake this as a period, but the bleeding is much too light and too early to be caused by the menstrual cycle.
References
- MayoClinic.com: Getting pregnant
- “Fertility and Sterility”; Plasma concentrations of human Chorionic Gonadptrophin from the time of implantation until the second week of pregnancy; Lenton E.A., Neal L.M. & Sulaiman R.; 1982
- Getting Pregnant: Charting Basics 1 - Basal Body Temperature
- Dr. Lam: Progesterone
- RnCeus.com: Estrogen
