The basal body temperature can drop before (a rise in estrogen) and after ovulation. In the second case, a decrease in BBT occurs due to implantation of the embryo, with hormonal imbalance, or before the beginning of the period. During pregnancy, a one-day drop in BBT rarely occurs (indicators are restored the next day). With a long drop (more than one day), you need to consult a doctor.
In this article, we will talk about why the basal body temperature drops at different periods of the cycle. This will help women, who are planning, to interpret correctly their BBT chart, as well as suggest how not to miss the tendrils of fear that our body sends. If you are interested to know why the basal body temperature drops – read on.
What affects the decrease of the basal body temperature?
The main natural factor for decreasing BBT is a high estrogen level or low progesterone level. As estrogen decreases, progesterone increases the temperature.
Normally, in the first phase of the cycle, a gradual increase of the first occurs with a significant rise 6–36 hours before the release of a mature egg. After ovulation, progesterone levels increase, which leads to an increase in BBT.
A drop in the BBT on any day of the cycle before ovulation is normal and should not disturb you. The main attention should be paid to the decrease in indicators after rupturing of the follicle (ovulation), that is, in the second phase of the cycle.
If the basal body temperature in the second phase of the cycle has decreased after ovulation and is not increasing, it means either there was no follicle rupture yet, or there was no progesterone growth. It is also possible that there was an influence of external factors (the use of vagitories, disturbance of the measurement regime, replacing the thermometer, etc.).
Advice(!): If it is probable that ovulation took place – you need to track the dynamics of the BBT for three to five days. If there is still no growth, the reason is a hormonal imbalance. In the case of a situational repeat, three or more cycles in a row, a doctor’s consultation is necessary.
If the basal body temperature drops before menstruation
At the end of the second phase of the cycle, most often after 10–13 days of life, the yellow hormone-secreting body (corpus luteum), which formed at the site of follicle rupture, gradually breaks down and stops the production of progesterone. From this moment, the BBT begins to decrease – this is normal.
When menstruation comes, the indicators return to the usual level of the first phase. If the BBT decreases before menstruation, somewhere in a day or two, fertilization most likely did not occur in this cycle.
If the basal body temperature drops and rises in different phases of the cycle
The first phase of the cycle
This behavior of the basal curve sometimes happens due to a rise in estrogen just before ovulation.
Most often, indicators decrease by 0.2-0.4 °C or 0.36–0.72 °F (one, maximum two days) and return to the usual cycle of the first phase. If you notice a similar drop about two weeks before the onset of menstruation – this is probably a sign of coming ovulation. This is the best time for active child planning.
The BBT always increases after ovulation.
The second phase of the cycle
A sharp drop and increase of the basal line in the second phase is possible in the case of an implantation dip. Most often it happens on the 7-10th day after the egg release (ovulation).
The temperature drops sharply by 0.2-0.4 °C (0.36–0.72 °F), and the next day it returns to normal for during the second phase or becomes even higher. However, such a drop in temperature during implantation does not always occur and not in all women.
Decrease in the basal body temperature during pregnancy – a reason to beware?
Normally, before the 13th week, the main «producer» of progesterone (a hormone that supports pregnancy) is the yellow hormone-secreting body. This is until the placenta is formed.
Indicators of BBT stay at the level during the second phase of the cycle, which indicates the normal level of hormones. If the basal body temperature has dropped before the end of the first trimester, this indicates a decrease in the amount of progesterone.
Note(!): Dropping of the BBT in the first trimester does not necessarily indicate that pregnancy is at risk due to a lack of progesterone. You need to observe the dynamics. You should act immediately only when there is a pain in the lower abdomen/lower back in combination with spotting.
During pregnancy, the BBT chart is informative only when measurements have been taken for three or more cycles in a row. In this case, the average indicators of the first and second phases in a particular woman are thoroughly known. In this case, you can objectively evaluate the work of hormones during pregnancy.
The normal difference between the phases is 0.3-0.5 °С or 0.54–0.9 °F and only it matters, not absolute indicators.
For example, during pregnancy, normal basal body temperature can be either 36.6 or 37.2 °C (97.88 or 98.96 °F). Their difference is important in comparison with the indicators of the first phase.