The Temperature (BBT) chart can give three pieces of information which are of use to the couple planning pregnancy (see also acheiving pregnancy):
The Temperature Chart can confirm ovulation.
The Temperature Chart can confirm ovulation did not occur.
The Temperature Chart can confirm pregnancy (Fig. 12-3).
(1) Temperature Chart (thermal shift) can confirm ovulation:
The rise in the basal body temperature (BBT) tells the woman that ovulation has occurred, (LINK to 12a for Fig. 12-1), and although this information is reassuring to the couple, from the point of view of achieving pregnancy it is of little use because once the thermal shift occurs the possibility of pregnancy decreases almost immediately as the ovum lives for just 24 hours and the fertilizable life of the ovum within that 24 hour period is from 8 to 12 hours. (ref 1, World Health Organization study).
The cervical mucus indicator defines the fertile phase of the cycle beforethe thermal shift occurs. Therefore to achieve pregnancy sexual intercourse should occur on those potentially fertile days leading up to ovulation when oestrogenic fertile-type mucus is present and in which sperm can survive for up to five days.2 (LINK to Ch. 15 to achieve pregnancy)
- (2) Temperature Chart can confirm ovulation did not occur in the cycle, (this is called an anovular cycle). (LINK to 12a for Fig.B 12-2). This information is also of use to the couple. Occasionally an anovular cycle may occur. However if anovular cycles are recurring the woman should consult her doctor.
- (3) Temperature Chart can confirm pregnancy (Fig. 12-3).
Fig. 12-3; The temperature chart can confirm pregnancy: Day 1 of the cycle marked on the bottom of the chart is the first day of the period (marked B). On Day 16 there is a rise in temperature and it remains elevated until Day 40 which is the last day shown on this chart. A higher-phase temperature that persists for 21 days or more indicates pregnancy. There is a further rise in temperature at the time of implantation on Day 24 due to the increase in progesterone secretion from the corpus luteum. The embryo implanting in the endometrium starts secreting human chorionic gonadotrophic hormone (hCG) which prevents the demise of the corpus luteum.3 Progesterone from the corpus luteum supports the pregnancy for 8 weeks after conception after which the embryo is capable of synthesizing all steroid hormones required for its development.3,4 (LINK to 6e for Fig. 6-17 diagram of implantation). Ovulation occurred sometime between Day 15 and Day 16.
IMPORTANT: The RULES of the ‘symptothermal double-check method’ of natural family planning regarding thermal shift interpretation, must be taught to the woman by a trained natural family planning teacher.
World Health Organization: WHO Task force on methods for the determination of the fertile period; temporal relationship between ovulation and defined changes in the concentration of plasma estradiol-17b, LH, FSH, and progesterone. Special Programme of Research, Development and Training in Human Reproduction. Am J Obstet Gynecol 1980; 138:383-390B
Klaus H; ‘Natural family planning – Is it scientific? Is it effective?’ page 4; Newman Lecture Series 1-May 21, 2000. ( internet if you google ‘natural family planning, Dr Hanna Klaus’).
Manassiev Nikolai, Whitehead, Malcolm; ‘Female Reproductive Health’; 2004, ISBN 1-85070-491-0
Griffin James E, Ojeda, Sergio R; ‘Textbook of Endocrine Physiology’;1996, p226-228; ISBN 0-19-510755-1(pbk)
To be most effective, the woman must be taught the Symptothermal Double-Check Method of Natural Family Planning by a qualified natural family planning teacher.