I just came across a seemingly amazing product, called Pearly or Lady Comp. This product was recently mentioned in Sweden's biggest newspaper.

According to the company, it can predict female fertility at the rate of 99.3% based on the menstruation cycle. This is higher than the preventive effect of birth-control.

The product: Lady Comp

Lady Comp is programmed with all available natural family planning research data and uses biomathematical forecasting calculations as well as the very latest computer techniques. LadyComp contains the first medical expertise to help provide safe, reliable and natural birth control.

The studies they reference: Clinical Studies

Are their claims true?

  • It seems slightly odd that there are no quoted studies since 1998 and some of the studies were not published.
    – Henry
    Sep 27, 2012 at 7:42
  • I suspect the numbers here are apples to oranges. It is hard to compare the introduction of a catalyst(semen) to the start of a reaction, versus withholding the catalyst. It is going to be much more effective to with hold than to inhibit the process. Especially with a process that is not terribly efficient in achieving reaction under normal conditions versus the perfect conditions the lab tests of birth control.
    – Chad
    Sep 27, 2012 at 12:41
  • Chad: Thanks for the comment. As I understand the studies, what has been done is to compare sexually active women that are using the LadyComp to know what days they should avoid sex and conventional birthcontrol, and see how many get pregnant anyways. To me, these metrics seem comparable, are they not? Sep 28, 2012 at 21:01
  • Is that 99.3% accuracy per measurement? Because that would mean that with 100 measurements you'd have 50.47% chance of at least one failure.
    – vartec
    Oct 28, 2013 at 22:30
  • I remember reading that some psychological effect can cause spontaneous ovulation in a women. (Can't find where) This would invalidate any predictability. Also irregular cycle exists and mess with such a thing.
    – MakorDal
    Oct 5, 2016 at 6:28

1 Answer 1


Yes, if the woman has reliable cycles and also pays attention to her cervical fluid.

When a woman ovulates, it intrinsically causes a rise in progesterone (this is known as the luteal phase). The presence of progesterone causes the body's basal temperature to rise by a few centigrade. Therefore, a slight raise in the BBT mid-cycle helps to confirm the beginning of the luteal phase, ie. ovulation. This 'temperature shift' pattern becomes predictable if the woman has consistent, normal cycles and so charting one's BBT (which is what the Lady Comp does for you) will give you a good idea of when to avoid sexual intercourse due to the foreseen ovulation. According to one study (1):

Basal temperature is an indirect measure of ovulation as a result of the progesterone-induced temperature increase of ∼0.3 °C from the follicular phase, when progesterone is low, to the luteal phase, when progesterone peaks following ovulation [7]. [...]∼75% of cycles had a temperature rise within 3 days of the LH surge [21].

I did not see anywhere on the Lady comp site, however, that cervical mucus is also documented. Lady Comp takes into account the cycle length and basal body temperature (BBT), which is quite similar to the natural family planning method of the book Taking Back your Fertility by Toni Weschler (http://www.tcoyf.com/), except the latter also observes and documents cervical fluid changes (also known as cervical mucus). To have such a high success rate in preventing pregnancy as Lady comp claims, cervical mucus must also be accounted for because different phases of the menstrual cycle correlate to different phases of cervical mucus, and this factor determines whether or not the sperm can travel up the female reproductive tract to actually reach the ovulated egg. In a study done on bovine to determine fertility properties of this mucus in mammals (2):

Cervical mucus becomes more plentiful, watery, less viscous and easier to traverse by spermatozoa in the follicular phase of the ovarian cycle, as well as under oestrogen administration. On the contrary, in the luteal phase of the cycle or under progesterone administration, this mucus becomes scanty, opalescent, viscous and, consequently, not favourable to sperm passage. Similarly, oviductal mucus becomes progressively less viscous during a short period after ovulation (Hunter 1995).

A close relationship between the rheological behaviour of bovine vaginal fluid obtained at oestrus and the molecular organization of its structural elements has been shown. During the course of oestrus, cervical mucus is able to achieve a dramatic reduction in its mechanical barrier effect while maintaining its three-dimensional filamentous structure. This structure is related to a low consistency index of samples, favouring sperm migration efficiency to the utmost. Taken together, all these findings suggest that in mid-oestrus (...), there seems only to be a short 2–4 h period (...) available for the sperm to reach the uterus. Either side of this time interval, the mucus is mechanically more hostile for the movement of sperm.

(1) Bedford J.L., Prior J.C., Hitchcock C.L., Barr S.I. Detecting evidence of luteal activity by least-squares quantitative basal temperature analysis against urinary progesterone metabolites and the effect of wake-time variability (2009) European Journal of Obstetrics Gynecology and Reproductive Biology, 146 (1) , pp. 76-80.

(2)Rutllant J, López-Béjar M, López-Gatius F. Ultrastructural and Rheological Properties of Bovine Vaginal Fluid and its Relation to Sperm Motility and Fertilization: a Review. Reproduction In Domestic Animals [serial online]. April 2005;40(2):79-86. Available from: Academic Search Premier, Ipswich, MA. Accessed January 4, 2013.

  • 1
    I am afraid this does not answer the question about Lady Comp at all. Lady Comp does not take cervical mucus into account. Its only input is menstruation and body temperature. Studies about sympto-thermal methods are therefore not relevant for it.
    – Suma
    Feb 4, 2018 at 19:26

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