Mittelschmerz

Mittelschmerz is one-sided lower abdominal pain that occurs at the time of ovulation, around the middle of the menstrual cycle, caused by stretching of the ovary by the growing follicle and irritation of the peritoneum by follicular fluid and blood after rupture. It affects many ovulating women, lasts a few hours to 2 days, and settles by itself. It matters because it is harmless but resembles serious conditions such as appendicitis, ectopic pregnancy and ovarian torsion.

• Risk factors: regular ovulatory cycles, younger age, previous episodes.
• Pain switches sides in different months in some women.
• Suppression of ovulation stops it.

Women have sudden dull or sharp pain in the lower abdomen on one side, around day 12 to 16 of the cycle, lasting from minutes to 48 hours, sometimes with light spotting, mild nausea and clear cervical mucus. There is no fever, and the pain is not constant.

• Mild tenderness on the affected side, no guarding or rebound.
• Recurring pattern in successive months.
• Differential diagnosis: ectopic pregnancy, appendicitis, ruptured or haemorrhagic ovarian cyst, ovarian torsion, pelvic inflammatory disease, endometriosis, urinary tract infection or stone, constipation, irritable bowel syndrome, early pregnancy complication.
• Complications: anxiety, missed work, misdiagnosis and unnecessary surgery, haemoperitoneum in rare cases of bleeding from the ruptured follicle.

The diagnosis is clinical, once other causes of pelvic pain are excluded.

• Menstrual and pain diary for 2 to 3 cycles showing midcycle pain; urine hCG to exclude pregnancy.
• Temperature, pulse, abdominal examination for peritonism; speculum and bimanual examination if pain is persistent.
• Transvaginal ultrasound (a small amount of free pelvic fluid, a collapsed follicle or corpus luteum is normal); full blood count and C-reactive protein if febrile.
• Urine dipstick; chlamydia and gonorrhoea tests if there is discharge or risk.

The principle is reassurance with simple analgesia, with suppression of ovulation only for severe recurring pain.

• Supportive: reassurance that the pain is normal and self limiting; heat pack on the lower abdomen; rest; light activity; pain and menstrual diary.
• Pharmacological: paracetamol 1 g oral 6-hourly (maximum 4 g in 24 hours); ibuprofen 400 mg oral 8-hourly with food for up to 3 days; combined oral contraceptive pill with ethinylestradiol 30 micrograms and levonorgestrel 150 micrograms oral once daily for 21 days then 7 days free, to suppress ovulation if pain is severe and recurrent; levonorgestrel 30 micrograms oral once daily for those who cannot take oestrogen.
• Procedures: none.
• Special groups: women with asthma sensitive to NSAIDs, peptic ulcer, kidney disease or on anticoagulants use paracetamol alone; women with a positive pregnancy test and pain need urgent ultrasound for ectopic pregnancy.
• Red flags: pain lasting more than 48 hours, fever above 38 degrees Celsius, vomiting, guarding or rebound, syncope, positive pregnancy test, heavy vaginal bleeding, systolic blood pressure below 90 mmHg.
• Follow-up: review at 3 months with diary; ultrasound if pain changes character, worsens or does not follow the cycle; review of contraceptive options.