Gravidity and Parity Definitions (and their Implications in Risk Assessment)

The precise definition of gravidity and parity varies slightly from country to country.
In the UK:¹

The current total fertility rate (the average number of children a woman would have if she experienced the fertility rate of a particular year for her entire child bearing years) stands at 1.78 (2004 figures)². Women are commencing their child bearing later and having less children in total.
Patterns of fertility in terms of parity have remained pretty constant in terms of percentage distribution (2002 figures)³ but this means that the actual numbers of grand multiparous women have fallen significantly:

Obstetric histories should always record parity, gravidity and outcomes of all previous pregnancies as:

• Outcomes of previous pregnancies give some indication of the likely outcome and degree of risk with the current pregnancy.
• The number of previous pregnancies and deliveries will also influence the risks associated with the current pregnancy.
• What is considered normal labour varies according to parity:
  • Normal labour in a prima gravida is significantly different to normal labour in multiparous women as physiologically the uterus is a less efficient organ and is frequently incoordinated or hypotonic. The average first stage in a prima gravida is significantly slower than in a multip (primarily due to the rate of cervical dilation)⁴ - so progress is expected to be slower but delay longer than expected should prompt augmentation in managed labour.
  • Interestingly, grand multips have a longer latent phase of labour than either nulliparous or lower-parity multiparous women but then begin to dilate more rapidly. After 6cm dilation, partogram curves for lower parity multips and grand multips are indistinguishable. Progress of labour does not appear to continue to improve with additional childbearing⁵.
• Psychological factors - good antenatal education, support during labour and pain control (if desired) are especially important in a first pregnancy as anxiety levels are likely to be high.

Risks associated with primiparity

• Higher risk of developing pre-eclampsia (relative risk 2.91 with confidence interval 1.28-6.61)⁶.
• Delayed first stage of labour (though this could be considered normal in a primip).

Risks associated with grand multiparity ⁷

• Increased likelihood of abnormal fetal presentation.
• Increased risk of precipitate delivery.
• Increased risk of uterine atony.
• Increased risk of placenta praevia.
• Increased risk of uterine rupture.
• Increased risk of amniotic fluid embolism.
• Increased risk of obstetric haemorrhage.
• Increased risk of stress incontinence and urinary urgency symptoms⁸.

What is a high risk pregnancy?

Risk equates to factors that increase likelihood of harm to mother or baby. There is no universally accepted definition of a 'high risk' pregnancy and nor can antenatal 'risk' screening identify every pregnancy/labour that will run into complications. Usually risk factors are combined and weighted to try to match an appropriate level of medical care and intervention to a more risky pregnancy to attempt to reduce the chances of a poor outcome.

Confounding variables ⁹

Increased parity is often associated with:

• Increasing maternal age.
• Lower socioeconomic and educational status.
• Poorer prenatal care (more likely to be late bookers and poor attenders).
• Smoking and alcohol consumption.
• Higher BMIs.
• Higher rates of gestational diabetes.

It is not always possible to dissociate the various risk factors attributable to each factor. In 1997-1999 the maternal mortality rate was almost 6 times greater in women of parity 4 or more as compared to that of women in their first pregnancy¹⁰ but in the subsequent report³, this apparent association between high parity and maternal mortality was discounted and the association becomes much harder to characterise as fewer and fewer women in the UK have 4 or more children into the 21st century. The lowest maternal mortality rates are observed in women with one previous pregnancy.

Primiparous women:

• Good antenatal care with particular vigilance to early warning signs of pre-eclampsia toxaemia (PET).
• Opportunities for antenatal and parenting education.
• NICE recommends nullips with uncomplicated pregnancies should have 10 routine antenatal appointments (versus 7 in parous women)¹.
• Where there is delay in the first stage of labour in a primip, active management with artificial rupture of membranes and/or oxytocin is usual to augment labour.

Grand multiparous women:

• Usually appropriate to book for delivery in a specialist unit
• Iron and folate prophylaxis
• Plan for care of existing children during admission
• Vigilance for abnormal fetal presentations from 36 weeks onward
• Plan for possible rapid labour and delivery
• Monitor strength of contractions and fetal presentation during delivery
• Plan for possibility of post partum haemorrhage
• Good physiotherapy and post-natal follow up for urogynaecological problems