Self-employed mothers cannot get Statutory Maternity Pay, so they claim Maternity Allowance instead. It pays up to GBP 194.32 a week (or 90% of average weekly earnings if lower) for 39 weeks. Pay too little Class 2 National Insurance and it drops to as little as GBP 27 a week.
Self-employed, 13+ weeks of Class 2 NI paid in the Test Period - The full rate: GBP 194.32 a week...
Self-employed, fewer than 13 weeks of Class 2 NI paid - A reduced rate scaled between GBP 27 and...
Self-employed, no Class 2 NI paid in the Test Period - The floor rate: GBP 27 a week for up to 39...
Can you fix a reduced rate? - Yes - HMRC can let you pay voluntary Class 2 NI for the Test Period...
Plus 7 more in the full guide

freedomisntfree.co.uk/guides/maternity-allowance-self-employed-uk