pregnancy induced hypertension

During pregnancy hypertension is defined as:

• diastolic blood pressure of 90 mmHg or more on two occasions more than 4 hours apart or
• a single diastolic blood pressure above 110 mmHg (1)

In pregnant women, hypertensive disorders may present as pre existing primary or secondary chronic hypertension or as new onset hypertension during the second half of the pregnancy (1).

• it is important to distinguish hypertension which antedates pregnancy from that in which it is an indicator of pre-eclampsia.

A BMJ review has suggested the following classification of hypertensive disorders in pregnancy:

• gestational hypertension (pregnancy induced hypertension)
  • hypertension detected for the first time after 20 weeks' gestation, in the absence of proteinuria (1,2,3)
  • hypertension defined as systolic blood pressure 140 mm Hg or diastolic blood pressure 90 mm Hg
  • resolves within three months after the birth
• pre-eclampsia and eclampsia**
  • hypertension and signicant proteinuria detected for the first time after 20 weeks' gestation (1,3)
  • hypertension defined as above Proteinuria defined as 300 mg/day or 30 mg/mmol in a single specimen or 1+ on dipstick
  • eclampsia is the occurrence of seizures superimposed on the syndrome of pre-eclampsia
• chronic hypertension - known hypertension before pregnancy; or a rise in blood pressure to more than 140 / 90 mmHg before 20 weeks
  • "Essential" hypertension if there is no underlying cause
  • "Secondary" hypertension if associated with underlying disease
• pre-eclampsia superimposed on chronic hypertension
  • Onset of new signs or symptoms of pre-eclampsia after 20 weeks' gestation in a woman with chronic hypertension

In the UK pre-eclampsia is characterised by raised blood pressure with proteinuria that develops after 20 weeks gestation. The latter category ('transient hypertension') in the UK is known as pregnancy induced hypertension.

** the UK British Hypertension Society have defined pre-eclampsia as (4):

• either a rise in blood pressure of >=15 mmHg diastolic or >= 30 mmHg systolic from early pregnancy
• or diastolic blood pressure of >= 90 mmHg on 2 occasions 4 hours apart or >= 110 mmHg on 1 occasion and proteinuria (1+ is an indication for referral and >=300mg/24 hours is a criterion for diagnosis)

NICE have defined pre-eclampsia as (3):

• NICE state that pe-eclampsia is new hypertension presenting after 20 weeks with significant proteinuria
  • significant proteinuria is diagnosed if the urinary protein:creatinine ratio is greater than 30 mg/mmol or a validated 24-hour urine collection result shows greater than 300 mg protein

A systematic review (5) found that, in pregnant women with mild to moderate hypertension, antihypertensive drugs reduce the risk of severe hypertension, but no other effects on maternal or perinatal outcomes were shown.

Reference:

• (1) Duley L et al. Management of pre-eclampsia. BMJ 2006; 332:463-8.
• (2) Roberts. Pre-eclampsia: more than pregnancy induced hypertension. Lancet 1993;341: 1447-1451
• (3) NICE (August 2010). Hypertension in pregnancy - the management of hypertensive disorders during pregnancy
• (4) Williams B, Poulter NR, Brown MJ, Davis M, McInnes GT, Potter JF, et al. Guidelines for management of hypertension: report of the fourth working party of the British Hypertension Society, 2004-BHS IV. J Hum Hypertens 2004;18: 139-8
• (5)Abalos E et al. Antihypertensive drug therapy for mild to moderate hypertension during pregnancy. Cochrane Database Syst Rev. 2007 Jan 24;(1):CD002252