Ms Williams said her caseload had steadily increased since she started five and a half years ago and she had to turn some women away because she didn't take more than five a month. She said the women were able to find other midwives in the area.
Ms Williams also spoke to a colleague who agreed demand for midwives was increasing, she said.
Nationally the 57,476 births during the year to March 2015 was the lowest number since 2004.
Emeritus professor Ian Pool of the University of Waikato said the decline was due to the increased age of child bearing women.
The most common child bearing age is between 25 and 34 and there has also been an increase of women giving birth between the ages of 35 and 44.
Women also had children at older ages in the past but those women often already had children. Now people were having their first child when they were older, said Dr Pool.
Since the mid-1970s, New Zealand's total fertility - or number of births per woman - had remained static at two births per woman but the age of first time mothers has shifted massively.
That shift had no precedent in history.
Statistics New Zealand analyst Anne Howard didn't think New Zealand's birth figures would continue dropping.
She said births per year had been fluctuating around the 60,000 per year mark and this was expected to continue.
The large number of women born in the 1960s were now past having children but a relatively large group of women born around 1990 are now reaching prime age for having children, she said.
