Exámenes prenatales y diagnóstico del embarazo

Vea también el separado Cuidado prenatal, Antenatal screening for Down's syndrome y Diagnóstico prenatal articles. This article cannot cover all areas of clinical practice associated with the proper care of pregnant women but gives an overview of important areas, based on the latest guidance. The National Institute for Health and Care Excellence (NICE) provides full advice on the routine care of healthy pregnant women. Antenatal care is now exclusively done in secondary care; it is unusual for the GP to have any role in routine antenatal care.¹

Diagnosis of pregnancy and calculation of gestational age¹

Pregnancy diagnosis

• Diagnosis of pregnancy is best confirmed using a urine-testing kit that determines the presence of beta human chorionic gonadotrophin (beta-hCG) and many women will use this method to confirm their pregnancy.

• Where the absence of menses is the only current indicator of early pregnancy, it is important to confirm pregnancy using a testing kit.

• Routine pregnancy testing is not provided by the NHS; tests should be bought.

Calculation of gestational age

• An early ultrasound scan should be offered at 11-14 weeks, to determine gestational age and detect multiple pregnancies. It may also be part of the screening for fetal anomalies when the nuchal translucency is measured. Accurate gestational age assessment helps optimal antenatal care by, for example, reducing unnecessary induction because a pregnancy is thought to be further progressed than it actually is.

• Crown-rump length is the best surrogate measure of gestational age in the first trimester.

• Pregnant women who present at or beyond 14 weeks of gestation should be offered an ultrasound scan to estimate gestational age, using head circumference or biparietal diameter. If the crown-rump length is above 84 mm, the gestational age should also be estimated using head circumference or biparietal diameter. By the second or third trimester, multiple parameters may be used, including biparietal diameter, head and abdominal circumference and femur length.

Frequency and number of antenatal assessments in uncomplicated pregnancies¹

• Nulliparous patients with uncomplicated pregnancies should be seen over a schedule of ten appointments.

• Parous women with uncomplicated pregnancies should be seen over a schedule of seven appointments.

The first antenatal appointment¹

Antenatal appointments largely take place in secondary care, rather than at the GP. NICE recommends that the first antenatal (booking) appointment takes place early in pregnancy (by 10+1 weeks, or within two weeks of contacting the service for those who make contact later than 9+0 weeks). Women who book their care late in pregnancy should be asked about the reasons for this, as it may reveal physical, psychological, or social issues which need to be considered when planning their care.

A longer appointment should be offered if needed, depending on medical, social, and emotional needs. Information must be imparted in a way the woman can understand and backed up with written information, so she is in a position to make informed choices regarding options and care in her pregnancy.

Factors increasing complexity include the misuse of substances, women aged under 20, women who experience domestic abuse, and recent migrants, asylum seekers, or refugees, as well as any other women who have difficulty reading or speaking English. There is a separate NICE guidance covering care for complex women.²

Information and advice which should be covered in the first appointment is detailed in the separate Cuidado prenatal artículo.

Examination routinely done at the first appointment includes:

• Measurement of weight and height in order to determine body mass index (BMI).

• Measurement of baseline blood pressure (BP).

• Testing of urine for glycosuria/proteinuria.

Pelvic examination

Routine antenatal pelvic examination is not recommended as it does not accurately assess gestational age, nor does it accurately predict preterm birth or cephalopelvic disproportion.

Breast examination

Routine breast examination is also not recommended.

Peso¹

The patient should be weighed at booking and her height measured so that BMI can be calculated as weight in kilograms/(height in metres)². This can be used as a baseline for future weighing where it is clinically indicated.

Routine weighing at antenatal appointments is no longer recommended unless there is a clinical indication.

Pruebas de orina¹³

• Test for asymptomatic bacteriuria early in pregnancy using dipstick testing; send midstream specimen of urine (MSU) if indirect test is positive.

• Test for proteinuria at each antenatal appointment (along with BP as part of regular surveillance for pre-eclampsia).

Gestational diabetes mellitus

Women with risk factors for gestational diabetes mellitus (GDM) should have an oral glucose tolerance test between 24+0 and 28+0 weeks. Risk factors include a BMI of 30 kg/m² or more at booking, a previous baby weighing 4.5 kg or more, previous GDM, a first-degree relative with diabetes and being of an ethnicity which has a high prevalence of diabetes.³

Ver el separado Pruebas de tolerancia a la glucosa y Diabetes gestacional artículos.

Presión arterial¹⁴⁵

• Measure BP at booking and at every subsequent appointment, using a device validated for risk in pregnancy.

Examen abdominal¹

• Offer abdominal palpation at all appointments after 36+0 weeks, to identify possible breech presentations; if this is suspected, an ultrasound should be arranged.

Ultrasonido

Offer an ultrasound examination:

• Early in pregnancy (between 11+2 and 14+1 weeks) to:

  • Determine gestational age.

  • Detect multiple pregnancies.

  • Be part of the screening process for Down's syndrome and other chromosomal anomalies, if the woman opts into this. Nuchal translucency is measured if screening desired.

• Scan for congenital and structural anomalies between 18+0 and 20+6 weeks.

• Further scanning would be guided by clinical findings during the antenatal care, or previously known risk factors.

Criteria for more specialised care⁶

The triennial confidential report of maternal and child health identifies many high-risk scenarios in pregnancy. There is a two-fold difference in maternal mortality rates amongst women from Black ethnic backgrounds and a slightly increased risk of mortality for women from Asian ethnic backgrounds compared to white women,

The top five causes of maternal deaths are:

1. Tromboembolismo venoso.

2. Cardiac disease.

3. COVID-19,

4. Mental health conditions.

5. Epilepsy and stroke.

91% of women who died in the period covered by this report faced multiple interrelated challenges. These included social services involvement, domestic abuse and deprivation.

Women with pre-existing medical morbidity should be seen in coordinated multidisciplinary medical and obstetric clinics. Although the following list is not exhaustive, these conditions can be associated with more adverse outcomes and warrant specialist opinion:

• Cardiac disease, including hipertensión.

• Enfermedad renal.

• Diabetes treated with insulin, or any other endocrinological disorder.

• Treated psychiatric disorder.

• Haematological disease including propensity to thromboembolism and autoimmune disorder, such as síndrome antifosfolípido.

• Epilepsia requiring anticonvulsant therapy.

• Any current or recently treated malignant disease.

• Significant respiratory impairment, including severe asthma.

• Problematic alcohol use.

• Regular/problematic use of drogas recreativas such as heroin, cocaine, crack, ecstasy, etc.

• Chronic viral infections - eg, VIH, virus de la hepatitis B (HBV), virus de la hepatitis C (HCV).

• Autoimmune disorders.

• Previous uterine surgery including caesarean section, myomectomy or cone biopsy.

• Women at higher risk of complications during pregnancy (eg, older than 40 years), smokers, very young mothers, and those without social support.

• Problems associated with previous pregnancies:

  • Aborto espontáneo recurrente (>3 consecutive pregnancy losses or a mid-trimester loss).

  • Parto prematuro.

  • Severe pre-eclampsia, HELLP syndrome (Haemolysis, EL (elevated liver) enzymes, LP (low platelet) count), or eclampsia.

  • Rhesus isoimmunisation or other significant blood group autoantibodies.

  • Anterior antepartum haemorrhage or postpartum haemorrhage on two occasions.

  • Retained placenta on two occasions.

  • Puerperal psychosis.

  • Grand multiparity (>6 children).

  • Previous stillbirth or neonatal death.

  • Small-for-gestational-age infant (<5th centile).

  • Large-for-gestational-age infant (>95th centile).

  • Baby weighing <2.5 kg or >4.5 kg.

  • Baby with a structural or chromosomal anomaly.