Mother's weight gain between initial assessment and birth, by BMI group at initial assessment and local health board

Variable filters

You will be able to change the filter selections once you've chosen how to view the data.
Year
10 of 10 selected
No values match your search
Area
10 of 10 selected
No values match your search
Mothers weight gain
3 of 3 selected
No values match your search
BMI group
4 of 4 selected
No values match your search
Data description

This indicates what a data value represents

2 of 2 selected
No values match your search

Choose how to view the data

You'll be asked to choose 2 variables to show on a table
The data will be shown with columns for each of the variables in the dataset, with a data value for all combinations of variables

Next update expected:August 2026

Updates

4th August 2026

This update includes the latest annual data.

19th December 2025
Dataset first published.

Main information

Designation
Accredited official statistics
Data provider
Digital Health and Care Wales (DHCW)
Data source
Maternity Indicators Dataset (MIDS)
Time period covered
January 2016 to December 2025
Dataset ID
bc054818-eaae-4505-b3ed-234c77ef14df

Overview

Summary of dataset and variables

Number and percentage of mother's weight gain between initial assessment and birth, by BMI group, broken down by local health board.

This data is derived from the Maternity Indicators dataset, provided to the Welsh Government by Digital Health and Care Wales (DHCW).

The Maternity Indicators dataset combines records from a mother’s initial assessment with a child’s birth record Full details of every data item available in the Maternity Indicators dataset are available through the NHS Wales Data Dictionary.

Data collection or calculation

Data from the Maternity Indicators dataset only includes initial assessment data where the initial assessment and birth both occurred in the same health board, in Wales only.

Data should include all hospital births and some home births; however, due to the way data is recorded, we are unable to distinguish between home and hospital births in some health boards. Births to Welsh resident mothers who gave birth in England or in any other country outside of Wales are not included in the data.

Data for each calendar year refers to when the baby was born for both birth and initial assessment statistics. Initial assessments may have taken place in the previous year but would be counted in the year in which the birth occurred. This ensures data throughout a single pregnancy is recorded in the same year.

The Wales-level percentage for pregnant women with BMI of 30 or greater are based on all records minus records with a ‘not stated’ or invalid value.

Records where BMI, height or weight are unrealistic values are classed as invalid, for example where BMI is less than 10 or greater than 100; where the pregnant woman’s weight is less than 30kg or more than 250kg; and where the pregnant woman’s height was less than 120cm or greater than 200cm.

The calculation also only includes women who had their initial assessment at 14 completed weeks of pregnancy or earlier. This is to reduce unfair comparisons where the BMI calculation is affected by baby growth where the initial assessment happened after 15 weeks. Between 11% to 15% of all pregnancies have been excluded for this reason in each year.

The number of records excluded can be found in Table 4 of the Maternity and birth statistics: quality report tables.

The Institute of Medicine (IOM) guidelines recommends a total weight gain of between 12.5 and 18kg for pregnant women with a BMI of less than 18.5 (‘underweight’); between 11.5 and 16kg for pregnant women with a BMI between 18.5 and 24.9 (‘normal weight range’); between 7 and 11.5kg for pregnant women with a BMI between 25 and 29.9 (‘overweight’); and between 5 and 9kg for pregnant women with a BMI 30 or more (‘obese’).

Statistical quality

For BMI, more than 90% of records had valid data for both height and weight data items, across all health boards, in most years apart from: Cwm Taf/Cwm Taf Morgannwg in 2016 (77%), 2019 (88%) and in 2024 (88%); Betsi Cadwaladr in 2019 (89%) and Aneurin Bevan in 2024 (23%).

In 2024, Aneurin Bevan has been excluded from analysis due to high levels of invalid data for height leading to 77% missing data for BMI. Data for Wales represents the 6 remaining health boards.

To calculate the amount of weight gained, each mother needs a valid weight recorded at initial assessment and between 36-38 weeks or at birth. There is a relatively high proportion of missing data for mothers’ weight at birth which limits the reliability of the weight gain data. From 2020 to 2023, Hywel Dda health board have provided little or no data for mother’s weight at birth. Swansea Bay provided little or no data from 2021 and 2025. As a result, the Wales data excludes these health boards. In 2024 Aneurin Bevan has been excluded as it has high levels of invalid data for weight at birth. As a result of the level of missing data, caution is advised when using this statistic.

From 1st April 2019 health service provision for residents of Bridgend local authority moved from Abertawe Bro Morgannwg to Cwm Taf. The health board names changed to Cwm Taf Morgannwg University Health Board and Swansea Bay University Health Board. Data for Abertawe Bro Morgannwg and Cwm Taf are available for previous years in this table. More detailed information on the sources of data and analyses in this statistical release are provided in the quality report.

Related reports

Published by

Organisation
Welsh Government
Contact email
stats.healthinfo@gov.wales