Obstetrics and Gynaecology: the pattern approach

Obstetrics and Gynaecology has a reputation for being a subject of lists: lists of antenatal visits, lists of causes of bleeding, lists of contraceptive methods, lists of cancer stages. Some of those lists carry numbers, and the numbers are where students lose sleep, because different books and different years seem to give different ones.

The good news is that OBG is also one of the most patterned subjects in the whole syllabus. The same few structures keep coming back. A pregnancy has a before, a during and an after. Bleeding follows a logic by timing and by pain. Hypertension in pregnancy runs on a small number of categories. Contraception sorts by mechanism and by who can't use what. Cancers share a staging rhythm.

If you learn the patterns first, you'll be able to hang the details on them, and you'll know which details are worth checking against an authoritative source. This article walks through the main patterns.

One caution runs through all of it. Schedules, screening intervals, drug dosages, staging revisions and national programme guidance change, and standard books don't always agree. Where this article describes a pattern and not a number, that is deliberate. Wherever a number matters for the exam, check your current textbook and the official NBEMS and NMC notices, and treat anything you can't confirm as unconfirmed.

Pattern one: the arc of a pregnancy

Think of antenatal care as a sequence of purposes, not a table of dates.

Booking. The first visit is about establishing the dating of the pregnancy, taking a history, examining, and running baseline investigations such as blood group and Rh status, haemoglobin, blood sugar screening and infection screening as per the national programme. It's also where you identify risk factors that will change how the pregnancy is managed.

Each visit after. Every routine visit asks a few repeating questions: how is the mother (blood pressure, weight, symptoms), how is the baby (fundal height, lie, presentation, heart rate, movements), and is anything needed (supplements, vaccines, counselling).

Supplements and prevention. Iron and folic acid, calcium, and tetanus protection are the classic themes. Folic acid is linked with prevention of neural tube defects. Rh-negative women who haven't developed antibodies need anti-D immunoglobulin to prevent sensitisation after events that can mix fetal and maternal blood. The exact timing and doses are programme details, so verify them.

Screening. The pattern here is "who gets screened for what, and when in pregnancy." Screening for gestational diabetes, anaemia, hypertension, infections and fetal anomalies each follows its own logic. Learn the why of each: what the test finds and what you do with a positive result. Learn the timings from your current source.

High-risk pregnancies. Rather than memorising a long list, group them: medical conditions (diabetes, hypertension, heart disease, anaemia, thyroid disease), obstetric history (previous caesarean, previous stillbirth, previous preterm birth), and current-pregnancy problems (multiple pregnancy, abnormal placentation, growth restriction). The question you ask of each group is "what extra monitoring or intervention does this need?"

Pattern two: labour as passage, passenger, powers

A reliable way to think about labour is to ask three questions: is the passage adequate (the bony pelvis and soft tissues), is the passenger in a favourable position (size, lie, presentation, attitude), and are the powers effective (the strength and coordination of contractions)? Most problems in labour come from one of these three, and the management follows.

Stages. The first stage runs from onset of true labour to full dilatation of the cervix. The second runs from full dilatation to delivery of the baby. The third runs from delivery of the baby to delivery of the placenta. Each stage has its own risks and its own care. Active management of the third stage exists to reduce postpartum haemorrhage.

Monitoring. The partograph is a chart that records progress and the condition of mother and baby over time so that delay or distress can be spotted early. Learn what it records and why, and the action it prompts, rather than the specific values drawn on a particular version of the chart.

Obstructed and prolonged labour. The pattern is a cause (passage, passenger or powers), recognition (slow progress, maternal exhaustion, signs of fetal distress), and a response (correct what can be corrected, or deliver by the safest route). In obstructed labour the dangers include uterine rupture, so know the warning signs.

Malpresentation and malposition. Learn the options for breech presentation and the reasons for choosing a route of delivery, the way to recognise a transverse lie, and why a transverse lie in labour is dangerous.

Caesarean section. Learn indications as a few families: problems with the passage, problems with the passenger, problems with the placenta, fetal compromise, and previous uterine scars. Then learn the complications in the same early and late grouping as in any surgery.

Pattern three: bleeding, sorted by when and whether it hurts

Bleeding is where OBG students feel most overwhelmed, because it appears in every phase. Break it down by timing first.

Early pregnancy. Bleeding in the first trimester raises the three classic possibilities: miscarriage in its various forms (threatened, inevitable, incomplete, complete, missed), ectopic pregnancy, and molar pregnancy. A woman of reproductive age with lower abdominal pain, a missed period and bleeding has an ectopic pregnancy until proven otherwise. A pregnancy test and an ultrasound are central, and a woman who is unstable needs resuscitation and urgent surgery.

Antepartum haemorrhage. Bleeding after the point of viability and before labour. Two causes are essential. Placenta praevia classically presents with painless, fresh, recurrent bleeding, and a vaginal examination in a woman with suspected praevia should not be done until the placental position is known, because it can provoke severe haemorrhage. Placental abruption classically presents with pain, a tender, hard uterus and bleeding that may be concealed, with the woman looking worse than the visible blood loss suggests. Risk factors include hypertension, trauma and a history of abruption. Keep the two side by side in a table; the contrast is what gets tested.

Postpartum haemorrhage. The common memory frame is the four Ts: tone (uterine atony, by far the commonest), trauma (tears, uterine rupture, inversion), tissue (retained placenta or membranes), and thrombin (coagulation problems). The principle of management is to resuscitate and treat the cause at the same time. Uterotonic drugs, uterine massage, repair of tears and removal of retained tissue each map to one T. Know the drug contraindications too. For example, some uterotonics are avoided in asthma and others in hypertension, and the reason is always in the pharmacology.

Gynaecological bleeding. Abnormal uterine bleeding is organised by the cause categories your textbook uses (structural causes such as polyps, fibroids and malignancy, and non-structural causes such as ovulatory disorders, coagulopathy and endometrial problems). The approach is the same as always: exclude pregnancy, find the category, treat accordingly. Postmenopausal bleeding is a different matter: it needs evaluation for endometrial pathology until shown otherwise.

Pattern four: hypertension in pregnancy

This topic is a gift to a pattern learner, because it's built from a small set of categories.

• Chronic hypertension: present before pregnancy or before a certain point in it.
• Gestational hypertension: new hypertension later in pregnancy without the features of pre-eclampsia.
• Pre-eclampsia: hypertension with evidence of organ involvement, such as protein in the urine or other maternal organ dysfunction.
• Eclampsia: pre-eclampsia with seizures.
• Superimposed pre-eclampsia: on top of chronic hypertension.

The exact blood pressure thresholds and the definition of "organ involvement" have been revised over the years, and books vary, so use the definition your current source gives and check it against the official guidance.

Management follows a pattern too. Control the blood pressure with drugs considered acceptable in pregnancy, commonly labetalol, nifedipine and methyldopa. Prevent and treat seizures with magnesium sulphate in severe disease and eclampsia. Know the signs of magnesium toxicity (loss of patellar reflexes, respiratory depression, reduced urine output) and that calcium gluconate is the antidote. Plan delivery, since delivery of the placenta is the definitive treatment, with the timing depending on severity and gestational age. Watch for complications such as HELLP syndrome (haemolysis, raised liver enzymes, low platelets), placental abruption, pulmonary oedema and renal injury.

Notice how few facts that really is: five categories, three treatment pillars, one antidote.

Pattern five: contraception by mechanism and by who can't use it

The contraception chapter has a lot of methods, so sort them two ways.

By mechanism and duration. Barrier methods block sperm. Hormonal methods (combined pills, progestin-only pills, injectables, implants, hormone-releasing devices) mainly suppress ovulation and alter cervical mucus and the endometrium. Copper intrauterine devices work mainly by being toxic to sperm and affecting implantation. Permanent methods are tubal occlusion and vasectomy. Within each group, ask: how long does it last, is it reversible, and what's the signature side effect?

By who can't use what. This is the exam-friendly view. Oestrogen-containing methods are avoided where there's a risk of clots or a condition where oestrogen is harmful: a history of venous thromboembolism, migraine with aura, active liver disease, certain cancers, and in older women who smoke. Progestin-only methods are often chosen when oestrogen is contraindicated. Intrauterine devices have their own cautions, such as pelvic infection and an abnormal uterine cavity. Learn the contraindications as a short list per method family, and compare against the national and international eligibility guidance your source uses.

Pattern six: the staging rhythm in gynaecological cancers

Cancers of the cervix, uterus, ovary, vulva and others each have a staging system, usually from FIGO (the international federation of gynaecology and obstetrics). Details differ, and the systems have been revised, in some cases quite recently, so learn the rhythm first and the details of the current edition second.

The rhythm is simple. Stage I: the cancer is confined to the organ where it started. Stage II: it has spread beyond that organ into neighbouring structures, but remains within a limited local region. Stage III: it has spread further, to regional lymph nodes or to wider areas in the pelvis or abdomen, depending on the cancer. Stage IV: it has spread to distant organs or to structures that mark advanced disease. Each stage then has substages with finer distinctions.

Two things to hold onto. First, the method of staging differs: some cancers have traditionally been staged clinically, some surgically, and recent revisions have allowed imaging and pathology to contribute more. Second, the stage drives management: early disease is often treated surgically, while more advanced disease relies more on radiotherapy, chemotherapy or both. Learn that gradient, then add the specific recommendations from your current source.

For each cancer, build one card with the same prompts: risk factors, usual presentation, how it's diagnosed, how it's staged, broad treatment by stage, and prevention or screening where relevant. Cervical cancer, for example, has a clear story: the role of persistent infection with high-risk human papillomavirus, screening to detect precancer, vaccination as prevention, and treatment that depends on stage. Ovarian cancer is the one that tends to present late, which is why the staging story is so tied to spread within the abdomen.

Pulling the patterns together

Exam questions in OBG are usually built on a presentation, so the skill is to name the pattern within seconds. Practise that directly. Take a mixed set of OBG questions and, before you answer, name the pattern. You can use NextPrep's practice questions, your own bank, or past questions you've collected from legitimate sources. Name the pattern first, then answer.

The short version

• OBG is a patterned subject. Learn the pattern, then the details.
• Antenatal care is a sequence of purposes: booking, routine visits, prevention, screening.
• Labour problems come from passage, passenger or powers.
• Sort bleeding by timing and by pain, and use the four Ts for postpartum haemorrhage.
• Hypertension in pregnancy is five categories, three treatment pillars and one antidote.
• Learn contraception by mechanism and by who can't use it.
• Learn the staging rhythm for gynaecological cancers, then the details of the current edition.
• For schedules, thresholds and syllabus, check current textbooks and the official NBEMS and NMC notices.

What to do this week

1. Draw one page per pattern (antenatal, labour, bleeding, hypertension, contraception, cancer staging) with only headings and the key contrasts.
2. Make a side-by-side table for placenta praevia versus placental abruption and for each type of miscarriage, using your standard textbook.
3. List five numbers you've seen in OBG sources that you are unsure about, and note which source gives which. Resolve them against the official guidance, or mark them as unconfirmed.
4. Do a mixed set of OBG questions and write the pattern name next to each before answering. Card the ones where you chose the wrong pattern.
5. Pick one gynaecological cancer and complete the six-prompt card for it from your textbook.