# Stages of pregnancy and birth

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**Obstetrics** is the study of pregnancy, childbirth and the postpartum period.

**Perinatal** is pregnancy and first 12 months after childbirth - *around (peri) birth (natus)*.

## Before birth

Terms to refer to **before birth** are:
* **Pregnancy** - *pre (before) birth (natus)*
* **Prenatal** - *before (pre) birth (natus)*
* **Antenatal** - *before (ante) birth (natus)*
* **Antepartum** - *before (ante) giving birth (partum)*

Pregnancy consists of three trimesters, or 3-month intervals - *three (tri) months (mensis)*:
* **1st trimester** (0-12 weeks)
* **2nd trimester** (13-28 weeks)
* **3rd trimester** (28 weeks-birth) [[source]](https://www.ekhuft.nhs.uk/services/during-your-pregnancy/pregnancy-timeline/)

As shared by Steve Thornton, the trimesters can also usually be referred to pregnancy divided into thirds:
* **1st trimester** (0-13 weeks)
* **2nd trimester** (13-26 weeks)
* **3rd trimester** (26-39 weeks, or delivery)

## Labour

Terms that refer to **giving birth** - from the onset through to delivery of the placenta:
* **Labour**
* **Intrapartum** - *within (intra) giving birth (partum)*

Stages of labour [[source]](https://www.nhs.uk/pregnancy/labour-and-birth/what-happens/the-stages-of-labour-and-birth/):
* **Latent stage** - usually the longest stage, cervix starts to soften and open (dilate), may being irregular contractions, may be hours or days until established labour
* **First stage (established labour)** - begins when cervix is dilated to about 4cm and contractions are stronger and more regular, ends when cervix is fully dilated (about 10cm). This stage is usually 8-18 hours for first pregnancy and 5-12 hours for second/third pregnancy
* **Second stage** - beings when cervix is fully dilated, ends with birth of baby. This stage is usually up to 3 hours for first pregnancy and up to 2 hours for second/third pregnancy
* **Third stage** - beings after the baby is born, and ends once placenta is delivered

## After birth

Terms to refer to **after birth** are:
* **Postpartum** - *after (post) giving birth (partum)*
* **Postnatal** - *after (post) birth(natus)*
* **Neonatal** - the neonatal period specifically refers to the first 28 days/4 weeks of a child's life, and the child is called the neonate or newborth - *new (neo) birth (natus)*

The length of the postpartum or postnatal period culturally varies, with some researchers believing it is up to six months.

## Age of the baby

There are several different ways that the baby's age will be measured:
* **Conceptional age** - time since day of conception. It is often used in context of assisted reproductive technologies since they can accurately define this date.
* **Gestational age** - time since first day of the last menstrual period - if baby was conceived using assisted reproductive technology, this is calculated by adding 2 weeks to the conceptional age. It is sometimes referred to as menstrual age (not recommended).
* **Chronological or post-natal age** - time since birth
* **Post-menstrual age** - gestational age + chronological age. This is often used during neonatal hospital admission.
* **Corrected age** - It is sometimes referred to as adjusted age (not recommended). It is the age of the child from the expected data of delivery, i.e. chronological age - number of weeks that were born before 40 weeks of gestation.

Since 'most women know when their last period began but not when ovulation occurred,' the gestational age is often 'used when estimating the date of delivery'.

[[source]](https://doi.org/10.1542/peds.2004-1915)

## Premature birth

* **Extremely pre-term** - born at or before 28 weeks gestation
* **Very pre-term** - born between 28 and 32 weeks gestation
* **Moderate to late pre-term** - born between 32 and 37 weeks gestation
* **Pre-term** - born before 37 weeks gestation
* **Term** - born at or after 37 weeks gestation

[[source]](https://www.bliss.org.uk/parents/in-hospital/about-neonatal-care/what-is-neonatal-care)