When to Take a Pregnancy Test

How many women have not made these questions before? Just a single sexual intercourse without the effective use of a contraceptive method so that the woman is at risk of becoming pregnant.


In this paper we discuss the following questions about pregnancy:

  •  What are the most reliable pregnancy tests.
  • When a pregnancy test is positive.
  • How many days of menstrual delay is due to the pregnancy test.
  • What are the symptoms of pregnancy.



The most reliable method to diagnose a pregnancy is blood dosage of a hormone called human chorionic gonadotropin (hCG). As we only dose the beta fraction of hCG, blood test used to diagnose pregnancy is called beta hCG (BHCG)

The beta hCG levels start to rise already eight days of fertilization, just after the implantation of the egg (sperm + egg) in the womb.


When to take a pregnancy test?

Most current home pregnancy tests can detect the presence of hCG in urine on the first day of missed period. However, the amount of hormone in the urine at such an early stage of pregnancy may be small, generating a questionable result (explain below). Therefore, the safest thing is to carry out the test after a week of missed period.

If you think you may be pregnant but her first test was negative, repeat it after one week. In this short time the hCG concentration reaches quadruple, reducing the risk of a false negative result.

There are on the market dozens of different types of pregnancy test. Some are better quality than others, being able to detect very small levels of hCG in urine. However, one week after missed menses, the amount of urinary hCG is already high enough for all pharmacy tests can detect the presence of the hormone.

What values ​​of beta hCG indicate pregnancy?


  •  – Beta values ​​below 5 mIU hCG / ml are negative, ie discard pregnancy.
  • – Values ​​between 5 and 25 mIU / ml are undefined and can mean very early pregnancy, when there was still time enough hormone to be produced to be detected in the blood. In these cases one must repeat the test after three days.
  • – Values ​​above 25 mIU / ml are positive and indicate ongoing pregnancy.

During the first thirty days, the value of beta hCG nearly doubles every 24-48 hours, reaching up to 150,000 mIU / ml at 10 weeks of gestation. Thereafter, its value falls, stabilizing around the 10,000 mIU / ml.

Beta hCG is dosed in laboratories through blood test. Most women, however, prefer more comfortable methods, which can be made at home and without the need for needles for drawing blood. Therefore, since the 1970s there are home pregnancy tests, the famous pregnancy tests sold in pharmacies. They are nothing more tapes that detect the hCG beta presence in urine.

As the beta hCG concentrations in urine are lower than in the blood, pharmacy pregnancy tests take a little longer to stay positive. While the beta hCG blood can already be positive on the first day of missed period, with beta testing urinary hCG are better when done after a week or two delay, to avoid false negatives. The more time is passed after conception, the greater the level of blood BHCG and hence urine. After two weeks of the menstrual period fails, the sensitivity of pharmacy test reaches 99%.


positive pregnancy test

In general, one can make the pharmacy pregnancy test on the first day of a missed period, however, it should be borne in mind the risk of a false negative result for the precocity of the examination. So if the pharmacy test done with little menstrual delay time is negative, it is necessary to repeat it after one week, if menstruation continues late, of course.



In more advanced pregnancies, we can identify the gestational sac (structure that houses the embryo) from the 5th week of pregnancy by transvaginal ultrasound or from the 7th week by abdominal ultrasound.

Amazingly some women do not seek diagnosis after advanced stages of pregnancy. Sometimes pregnancy is so obvious that we can identify it by physical examination. Twelve weeks, the uterus begins to be palpable and after 20 weeks we can already identify fetal heartbeat with a stethoscope, as well as realize their movements by abdominal palpation.

Early diagnosis of pregnancy is important to immediately get prenatal care. Besides controlling blood pressure, glucose levels, recognition of pregnancy it is important to avoid ingestion of alcohol and drugs that could be harmful to the fetus.


It is always good to remember that the correct use of contraceptives confers protection more efficiently than 99%. If you take the pill correctly, the chance of getting pregnant is almost nil.


Yes, they help, but you can not make the diagnosis of pregnancy based only on signs and symptoms. Knowing the symptoms of pregnancy is important for the woman to feel encouraged to make a diagnosis of pregnancy tests. However, in some way, the presence or absence of these signals serves to confirm or discard an ongoing pregnancy.

The signs and symptoms of pregnancy that should light a warning light for women of childbearing age who have had unprotected sex in the last weeks are:

a) menstrual delay

The most obvious symptom of pregnancy is a missed period. Every woman of childbearing age, sexually active with delayed longer period than a week should consider pregnancy.

However, not all women can easily identify a delay in menstruation. There are women with irregular ovulatory cycles that sometimes are up to two months without menstruating. Another problem is that some pregnant present small cyclical bleeding in early pregnancy, leading them to think that it is just a weaker period. There is also the possibility of a little bleeding during the implantation of the embryo in the uterine wall. This deployment is usually ten to fourteen days after fertilization, at about the time that menstruation was to come, and may also cause confusion.


 b) Nausea and vomiting

A classic symptom of pregnancy are nausea and vomiting during the 6th and 12th weeks of pregnancy. The frame tends to be worse in the morning and improve throughout the day. The nausea can last up to 20 weeks of pregnancy.

 c) Sore breasts and swollen

The beta hCG and increased estrogen and progesterone promote stimulation of the mammary glands, leading to increased volume of the breasts, local pain and nipple darkening. In some women these changes are early, while others only notice changes in the breasts after a few weeks of missed period.

d) Tiredness

Most common in the first trimester, fatigue is probably caused by an increase in progesterone levels. Women who exercise regularly begin to notice a decrease in your strength, not tolerating the same exercise load that was previously. Sedentary women may be tired with little effort, such as climbing a flight of stairs or dishwasher.

 e) frequent urine

A frequent urge to urinate, usually associated with sleep disruption and the need to get up at night to pee, is common. This happens for changes in renal system, mainly by increasing the excretion of sodium (salt).

 f) Other common symptoms of pregnancy

Wishes and food aversions

– Mood swings

– Constipation

– Heartburn

– Dizziness

– Headaches (read: HEADACHE | Migraine and severity of signs )

– Lower back pain