Cycle and conception

The cycle is not a clockwork mechanism, and in very few women does ovulation fall on day 14. If you want to become pregnant, you gain most from understanding what actually happens over those four weeks – and from knowing when waiting stops being the best strategy.

What happens in a cycle

A cycle begins on the first day of bleeding and ends on the day before the next one. It falls into two halves that differ fundamentally: the first is elastic, the second is not.

In the follicular phase, several follicles mature under the influence of follicle-stimulating hormone (FSH). One prevails, grows to about two centimetres and produces increasing amounts of oestrogen as it does so. The oestrogen rebuilds the lining of the womb that was shed with the bleeding, and changes the mucus at the cervix: it becomes clear, stretchy and permeable to sperm. This phase lasts nine days in some women and twenty in others – it is what explains different cycle lengths.

Once oestrogen exceeds a threshold, the pituitary gland releases a sudden surge of luteinising hormone. This LH surge triggers ovulation around 36 hours later. The egg is picked up by the funnel of the fallopian tube and can then be fertilised for about twelve to eighteen hours – a very short window.

What remains of the follicle becomes the corpus luteum and produces progesterone. This hormone transforms the lining so that an embryo can implant, and keeps body temperature about 0.3 degrees higher. This luteal phase is remarkably constant: in almost all women it lasts twelve to fourteen days. If no pregnancy occurs, the corpus luteum breaks down, progesterone falls, the lining detaches – and the next bleeding begins.

Why ovulation is rarely on day 14

The number 14 comes from the model cycle of 28 days, and it persists stubbornly. In fact only a minority of women have a 28-day cycle, and even in them ovulation varies by several days from month to month.

Ovulation therefore cannot be calculated forwards from the start of the cycle, but backwards from the end: subtract the length of your luteal phase, as a rule fourteen days, from your cycle length. In a 32-day cycle ovulation therefore falls around day 18, in a 24-day cycle around day 10. That is exactly how the ovulation calculator works, using your own cycle length – not the one from the textbook.

The fertile window

What matters is not the day of ovulation but the days before it. Sperm survive in receptive cervical mucus for up to five days; the egg does not survive a whole day. The fertile window therefore runs from about five days before ovulation to the day after it – roughly six days a month.

The chances are highest on the two days immediately before ovulation. Anyone starting on the day after ovulation is already too late. In practice that means: intercourse every other day across the whole window is statistically the same as daily intercourse, and for most couples easier to keep up. Timed intercourse to a plan over many months, by contrast, often burdens the relationship more than it helps.

How to recognise ovulation yourself

• Cervical mucus. The most reliable sign without any equipment. Shortly before ovulation it becomes clear, glassy and stretches into threads – rather like raw egg white. The last day with this mucus is statistically the closest to ovulation.
• Basal body temperature. Measured in the morning before getting up, it rises by about 0.3 degrees after ovulation and stays raised until the bleeding. It therefore shows ovulation reliably – but only in retrospect. For timing intercourse it is useful only across several cycles; for confirming that ovulation took place, it is very good.
• LH tests from the pharmacy. They show the LH surge, so about a day before ovulation. Start testing a few days before the calculated date. In some women, especially with PCOS, baseline LH is permanently raised – the tests are then hard to interpret.
• Mittelschmerz. A dragging pain on one side of the lower abdomen, which about one woman in four notices. Too imprecise on its own, but usable as confirmation alongside other signs.

How long it normally takes

Even when everything is in order, not every cycle results in a pregnancy. Per cycle, the chance for a healthy couple is around 20 to 25 per cent. Over time that produces a picture that reassures many couples:

• after three months about 50 in 100 couples are pregnant,
• after six months about 70 in 100,
• after twelve months about 85 in 100.

Four out of five couples who are not pregnant after a year will be in the second year without any treatment at all. These figures apply to women up to their mid-thirties; as age rises, the chance per cycle falls and the time to pregnancy lengthens.

When assessment makes sense

The internationally usual threshold is: after twelve months of regular, unprotected intercourse without a pregnancy. From the age of 35 this is shortened to six months, because time is then itself a factor.

Regardless of that deadline, there are situations in which waiting is not worthwhile and assessment makes sense straight away:

• cycles shorter than 21 or longer than 35 days, or strongly fluctuating cycles,
• absent bleeding over several months,
• severe period pain or pain during intercourse – a possible sign of endometriosis,
• two or more miscarriages,
• known tubal infection, chlamydia infection or surgery in the pelvis,
• thyroid disease, diabetes or known polycystic ovary syndrome,
• age over 38.

What can disturb the cycle

Polycystic ovary syndrome

The commonest hormonal cause of difficulty conceiving. Typical are long or absent cycles, many small follicles on ultrasound and raised male hormones in the laboratory; insulin resistance is frequently present as well. Not every woman with PCOS is overweight, and not every one has increased body hair. Treatment starts with weight and exercise – a loss of just five to ten per cent restores ovulation in many women – and only then with medication to trigger ovulation.

Thyroid

An underactive thyroid lengthens cycles, raises the risk of miscarriage and is easy to treat. When trying to conceive, a lower TSH target applies than otherwise, as a rule below 2.5 mU/l. The value belongs among the first blood tests and is one of the most rewarding investigations there is.

Endometriosis

Lining of the womb outside the uterus, which responds to the cycle and can leave adhesions behind. The cardinal symptoms are severe and increasing period pain, pain during intercourse and discomfort on opening the bowels during the bleeding. On average it still takes several years to reach the diagnosis – a reason to take pain seriously rather than dismiss it as normal.

Shortened luteal phase

If fewer than ten days lie between the temperature rise and the bleeding, there may not be enough time for implantation. Behind this usually lies a weak maturation of the egg in the first half of the cycle, rather than an isolated progesterone deficiency – which is why the cycle is treated as a whole.

Prolactin and stress

A raised prolactin level suppresses ovulation. Causes range from medication through an underactive thyroid to a benign tumour of the pituitary gland. Marked underweight, excessive endurance training and sustained stress can also shut down the control coming from the brain.

Preparing for a pregnancy

Some things only work if they were started early enough. Four points are worthwhile as soon as you want to conceive:

• Folic acid. 400 micrograms daily, beginning at least four weeks before conception and continuing to the end of the twelfth week. The neural tube closes around day 28 – at a time when many women do not yet know they are pregnant. After a child with a neural tube defect, or with certain medications, a higher dose applies.
• Iodine. Austria is no longer a pronounced deficiency area, but the requirement rises considerably in pregnancy. 150 to 200 micrograms daily are usual, except with certain thyroid conditions.
• Rubella and varicella protection. Both are live vaccines and are not possible during pregnancy. If protection is missing it has to be topped up beforehand – with a month’s gap before conception. There is more on this under rubella.
• Smoking and alcohol. Smoking measurably lowers the fertility of both partners and brings the menopause forward by one to two years. For alcohol there is no established safe amount in pregnancy.

Also worthwhile are a blood count with ferritin, the vitamin D level, the TSH value and – depending on your history – a chlamydia swab. If you take medication regularly, have it clarified beforehand whether it can be continued in pregnancy; that applies particularly to epilepsy, high blood pressure and rheumatic disease.

The man is part of this

In about half of all couples having difficulty conceiving, at least part of the cause lies with the man, and in about a quarter it lies with him alone. The semen analysis is the simplest, cheapest and least burdensome examination in the whole assessment – and is still often done last. It belongs at the beginning, not at the end. A single abnormal result says little; what counts is the repeat after about twelve weeks, because that is how long sperm production takes.

What age means

The number of eggs is fixed at birth and declines throughout life; their quality declines with it. The chance per cycle is around 25 per cent in the early twenties, about 15 at 35 and under 10 per cent at 40. At the same time the proportion of miscarriages rises, because chromosomal errors become more frequent.

Anti-Müllerian hormone gives information about the remaining egg reserve. It is a useful value for planning treatment – but not a test that predicts whether a woman will conceive naturally. A low value in a 32-year-old with a regular cycle is no reason to panic, and a high value in a 43-year-old is no reason for reassurance.

What happens at the practice

It begins with a detailed conversation: the pattern of your cycles, previous illnesses, operations, medication, earlier pregnancies, work and strain. Then follow an ultrasound of the uterus and ovaries, a hormone profile at the start of the cycle and – where the cycle length makes it sensible – a progesterone measurement in the second half of the cycle as evidence that ovulation took place.

If a treatable cause emerges – thyroid, prolactin, absent ovulation with PCOS – that is treated first. If more is needed, such as a check of tubal patency or treatment with hormones to mature the eggs, referral to a fertility centre follows. As a private gynaecologist I accompany the assessment and the time before and after it; the reproductive medicine itself takes place there.

Weight, diet, exercise

The relationship between body weight and fertility runs in both directions. With a BMI over 30, cycles are more often irregular, the chance per cycle falls and the risk of gestational diabetes and high blood pressure rises. With a BMI under 18.5 the body sometimes stops maturing eggs altogether – a protective mechanism regularly seen in competitive athletes and in eating disorders. In both directions, moderate corrections are often enough: five to ten per cent of body weight makes a greater hormonal difference than any diet promises.

On diet there is less established evidence than the book market suggests. Best supported is a Mediterranean pattern: vegetables, pulses, wholegrains, olive oil, fish, little heavily processed meat. Endurance exercise in moderation has a favourable effect, while very intensive training over many hours a week can disturb the cycle. Coffee in usual amounts – up to about two or three cups a day – is regarded as harmless.

What cycle apps can and cannot do

Apps are good at collecting data and bad at predicting ovulation. If you enter only the start of bleeding and the cycle length, you get a calculation, not a measurement – the app assumes a constant first half of the cycle, and that is precisely the variable one. It becomes more reliable as soon as real observations are included: basal temperature, cervical mucus, LH tests. Some apps work to the symptothermal method and evaluate both together; they then identify ovulation reliably in retrospect.

Two things are worth knowing. First, a cycle app for contraception is something completely different from an app for planning – an imprecise prediction costs a month when you are trying to conceive, and a pregnancy when you are trying not to. Second, cycle data are health data. It is worth checking before you sign up where they are stored and to whom they may be passed on.

After a miscarriage

About one in four recognised pregnancies ends in miscarriage, the great majority in the first twelve weeks. The cause is predominantly a random chromosomal error in the egg or the embryo – nothing the woman caused or could have prevented. Neither sport nor work, stress, travel or intercourse triggers an early miscarriage.

After a single miscarriage the outlook for a subsequent healthy pregnancy is unchanged, and there is no medical reason to wait several cycles – as soon as you feel ready, nothing speaks against it. Targeted assessment is recommended after two consecutive miscarriages; it includes thyroid values, clotting, an assessment of the uterine cavity and – depending on the situation – a chromosome analysis of both partners. What is often missing in this time is not the diagnostics but someone who listens; time is set aside for that here too.

Where to go from here

Anyone who knows their own cycle has already covered most of the ground. A good start is to note the beginning of bleeding for three cycles and – if you like – the mucus as well, and to work out your own fertile window from that: ovulation calculator. When the time comes, the due date calculator works out the date. For everything in between: make an appointment.