The soonest possible time that pregnancy can be detected depends on how attentive the woman is to the signs and symptoms of pregnancy, especially after a first missed menstruation following unprotected sexual intercourse. Although there are stories we hear in social media of a woman having no knowledge or whatsoever that they are pregnant. This usually occurs in women who have irregular menstrual cycles. However, clinically in couples who are planning to get pregnant and are constantly monitoring any progress, considering that the woman has a regular cycle of menstruation, confirmation of pregnancy can take place right away.
Human chorionic gonadotropin (hCG) has always been used as the indicator for pregnancy, although nowadays this hormone has more treatment usage than what was previously believed. Every month, after the process of ovulation, an egg of a woman is pushed down to the fallopian tube where it awaits a sperm cell. Fertilization of the egg then takes place in the fallopian tube of the woman and can stay there for the next 3-4 days. The fertilized egg then travels down to the uterus for implantation, this time as a ball of dividing cells known as a blastocyst.
Once it adheres itself to the wall of the uterus, the trophoblastic cells release hCG to the maternal circulation. Human chorionic gonadotropin appears in increasing levels in the maternal circulation every week. It can be detected in the maternal blood 8 days after conception and in the urine 6-12 days (on an average of 9 days) after fertilization. Levels reach its peaks at 8-10 weeks of pregnancy. Over the counter pregnancy tests, which arrived on the market in 1976, are commonly used to detect the presence of hCG in the urine. But it wasn’t that easy to use before. It needed a test tube and a test tube holder (and a special mirror so they can read the results from the bottom!) for women to test their urine at home, and they needed to wait for 2 hours for the results.
Even worse than that, before 1976 diagnosis of pregnancy was done by injecting an amount of the woman’s urine into an immature female mouse or rabbit. Ovaries of these animals were then examined a few days later for the presence of follicular maturation, luteinisation, and hemorrhage into the ovarian stroma (poor mouse!). Fortunately, now it only takes seconds and a drop or two of urine on a manufactured strip for women to know if they are pregnant or not. If you ask how these strips detect hCG, well it uses certain antibodies (monoclonal or polyclonal antibodies) to know the presence of human chorionic gonadotropin.
There are, however, false negative results in pregnancy. If we think about it, this might probably because of the inability of the pregnancy kits to detect levels of hCG. In a study done by Gnoth and Johnson (2014), they tested the accuracy of 9 over the counter pregnancy kits based on their claims of detecting pregnancy 8 days earlier or “can detect 10 mlU/ml” (usual detectable range of hCG in urine is 25mlU/ml in every urine sample). The study found that 4 tests were able to detect 25 mlU/ml of hCG and therefore consistent with the manufacturers’ claims.
One kit, however, had a 40% error of detection which is quite big, 1 kit gave a false negative result even if it claimed to detect 25mlU/ml, another one detected up to 50 mlU/ml of hCG, and the last 2 kits claimed to detect 10mlU/ml of the hormone, but the actual results were not consistent with the manufacturers’ claims of accurate and early detection. Poor recollections of a woman’s last menstrual period can also be a factor in the inability to detect pregnancy right away in pregnancy. Concentrations of human chorionic gonadotropin can be calculated and therefore tested by ascertaining the last menstrual period of the woman.
In addition to that, certain reasons why women may not have a reliable LMP date include, bleeding in the early pregnancy, current use of hormonal contraceptives, or when the mother is breastfeeding. There are also reported cases where women did not have any knowledge of whatsoever with regards to them being pregnant at the moment. In an article by BBC, it mentioned in an interview with a consultant obstetrician who said that irregularities of menstrual periods, the weight of the mother or denial may be reasons of such unawareness. Also, knowledge of the mother with regards to signs and symptoms of pregnancy can also be a factor.
In summary to all information presented, detection of pregnancy is multifactorial. It needs the proper time period based on the last menstrual period of the mother, it needs the proper over the counter pregnancy kit, the proper detection of signs and symptoms of pregnancy, a visit to the doctor, and lastly a confirmation on diagnostic or laboratory exams.
Author: Sarah Catina RN
Gnoth, S. & Johnson, S. (2014). Strips of hope: Accuracy of home pregnancy tests and new developments. Geburtshilfe Frauenheilkd. 74(7): 661-669.