I'm a bit confused about the length of time MA is usually paid for, for those who meet both the standard number of weeks and level of income requirements. The HMRC website says the norm is to be paid it for only 26 weeks www.hmrc.gov.uk/nic/maternity-all.htm, and doesn't mention 39 weeks on the page at all. However, other government sites such as direct.gov, and the Dept. of Work & Pensions say MA can be paid for up to 39 weeks, which is the same as SMP.
Is the HMRC site a bit out of date? I know it is not always well-maintained; I emailed them a couple of months ago to point out that they were showing incorrect tax bands, and would they sort it out.
(On an unrelated issue, just looking at the income tax pages now, I see that HMRC says the starting rate of income tax for savings is £0-£2,230, whereas direct.gov says £1 to £2,320 (a difference of £90). You'd think they could sort that out wouldn't you...)