Traditionally, one looks at planets in the Fifth House. Generally, having the Moon there is good for making babies. Saturn or Uranus, not so much. But of course one must also factor in house placements, difficult or supportive aspects to planets in the Fifth, the condition of the ruler of the Fifth House, and so on.
As with so many things in life, pinning these things down to one or two simple rules is difficult to do. And whenever I find an exception to that, I'm grateful. Here's one of those times:
Fertility appears to follow two cycles. One is the obvious one: your monthly cycle. If you're trying to conceive and haven't been able to for a while, you've likely gone through the whole procedure of charting your fertile days, making your man wear boxer shorts, and on and on. Astrologically, it appears there is a second cycle to be aware of.
Have a look at your own birth chart. Note the angle between the Sun and Moon, regardless of the signs involved. If you have Sun opposition Moon, you were born on a Full Moon. If you have Sun Conjunct Moon, you were born on the New Moon. If you have Sun square Moon, you were born on the half Moon, and so on.
Take that calendar you've got with the red check marks on your fertile days and look at the Moon phase... again, regardless of sign placement. When the Sun and Moon are about the same distance apart in the sky as they were when you were born, all else being equal, you are more likely to conceive. So if you have Sun sextile Moon in your birth chart, you are most likely to get pregnant if you have sex on a "fertile" day (according to your measurements) which falls four or five days before OR after the Full Moon.
Now: have fun making a baby. And if my advice works for you... Matthew isn't a bad name for a boy, is it?