Obstetric Terminology
The guidelines recommend management of common obstetric conditions at primary and referral level, based on local experience and evidence-based practice. They are not intended as strict protocols nor as standard operating procedures, but rather as a guide to safe effective management of common obstetric problems. The guidelines should be most useful to interns, medical officers and registrars.
Maternal age
An age of ≥35 years at conception is termed ‘advanced maternal age’ because of increasing likelihood of trisomies in the offspring, & increased risk of maternal medical disorders, such as hypertension, diabetes & thromboembolism.
Notes on teenage pregnancy:
- Pregnancy at ≤19 years is termed ‘teenage pregnancy’
- Pregnancy at age <18 years (minors) is of special interest as this is a school-going age group. According to the law, minors aged 12-17 years may sign consent for surgery and anaesthesia, but should be assisted in doing so by an adult guardian
- Pregnancy at age <16 years may result from rape, & raises social and family issues. All pregnant women aged <16 years should be referred to a social worker
Gestational age
Gestational age is calculated from the first day of the last menstrual period in a 28-day cycle. Using this method, the estimated date of delivery is calculated as: (date of first day of last menstrual period) + 9 months + 1 week (Naegele’s rule).
Gestational age is expressed in weeks as the number of completed weeks of gestation using the first day of the last menstrual period as the reference point.
Gestational age is:
- Preterm at <37 weeks (i.e. up to 36 weeks, 6 days)
- Term at 37-41 weeks (from 37 weeks, 0 days to 41 weeks, 6 days)
- Postterm at ≥42 weeks
There is no legal gestational age threshold for viability, although South African law considers stillbirths <28 weeks (26 weeks of intrauterine life) to be miscarriages (not for registration as deaths). The World Health Organization however defines miscarriages as pregnancies ending at <22 weeks of gestation.
Birth weights
Birth weights can be classified as follows:
- ≥4000 g: macrosomia
- <2500 g: low birth weight
- <1500 g: very low birth weight
- <1000 g: extremely low birth weight
There is no legal birth weight threshold for viability. All infants born alive receive care, but neonatal mortality rates are high at <800 g in South African referral hospitals. Babies <800 g do not usually qualify for ventilator support in neonatal care units.
Parity and gravidity
Parity refers to the number of pregnancies a woman has completed that have reached viability (approximately 26 weeks’ gestation), irrespective of whether the babies were born alive or dead. For example, a woman who has had one miscarriage at 14 weeks, one stillbirth at term and one preterm birth at 32 weeks of a baby that is still alive, has a parity of 2 (para 2 or P2). If this same woman then becomes pregnant, she remains para 2 until she has given birth, & only then (provided birth occurs after 26 weeks) does she become para 3. A completed twin pregnancy should be considered as a single parity (disputed by some authorities who believe a completed twin pregnancy confers two parities).
Gravidity refers to the number of pregnancies, irrespective of gestational age or completion, that a woman has had. For example, a woman who has had one previous ectopic pregnancy, one previous miscarriage and two normal term births, and who is now 11 weeks pregnant, has a gravidity of 5 (gravid 5 or G5). She also has a parity of 2, and can be termed a para 2 gravida 5 (P2G5).
The following terms are derived from the above definitions:
- Gravida – a pregnant woman (rarely used)
- Nulligravida – woman who has is not and has never been pregnant
- Unigravida – woman who is pregnant for the first time (rarely used)
- Multigravida – woman who has had two or more pregnancies (rarely used)
- Nullipara – woman who has never given birth at a viable gestational age
- Primigravida – woman who is pregnant for the first time
- Primipara – woman who has given birth to her first baby at a viable gestational age (a ‘primip’)
- Unipara – woman who has had one pregnancy completed at a viable gestational age (rarely used)
- Multipara – woman who has had 2 or more births at a viable gestational age (often used to include also women with only one birth – any ‘non-nullipara’)
- Grand multipara – woman who has had 5 or more births at a viable gestational age
- Great grand multipara – woman who has had 10 or more births at a viable gestational age