function pregnancyCalc(pregform) {
menstrual = new Date(); // creates new date objects
ovulation = new Date();
duedate = new Date();
today = new Date();
cycle = 0, luteal = 0; // sets variables to invalid state ==> 0

if (isValidDate(pregform.menstrual.value)) { // Validates menstual date
menstrualinput = new Date(pregform.menstrual.value);
menstrual.setTime(menstrualinput.getTime())
}
else return false; // otherwise exits

cycle = (pregform.cycle.value == "" ? 28 : pregform.cycle.value); // defaults to 28
// validates cycle range, from 22 to 45
if (pregform.cycle.value != "" && (pregform.cycle.value < 22 || pregform.cycle.value > 45)) {
alert("Your cycle length is either too short or too long for \n"
+ "calculations to be very accurate!  We will still try to \n"
+ "complete the calculation with the figure you entered. ");
}

luteal = (pregform.luteal.value == "" ? 14 : pregform.luteal.value); // defaults to 14
// validates luteal range, from 9 to 16
if (pregform.luteal.value != "" && (pregform.luteal.value < 9 || pregform.luteal.value > 16)) {
alert("Your luteal phase length is either too short or too long for \n"
+ "calculations to be very accurate!  We will still try to complete \n"
+ "the calculation with the figure you entered. ");
}

// sets ovulation date to menstrual date + cycle days - luteal days
// the '*86400000' is necessary because date objects track time
// in milliseconds;  86400000 milliseconds equals one day
ovulation.setTime(menstrual.getTime() + (cycle*86400000) - (luteal*86400000));
pregform.conception.value = dispDate(ovulation);

// sets due date to ovulation date plus 266 days
duedate.setTime(ovulation.getTime() + 266*86400000);
pregform.duedate.value = dispDate(duedate);

// sets fetal age to 14 + 266 (pregnancy time) - time left
var fetalage = 14 + 266 - ((duedate - today) / 86400000);
weeks = parseInt(fetalage / 7); // sets weeks to whole number of weeks
days = Math.floor(fetalage % 7); // sets days to the whole number remainder

// fetal age message, automatically includes 's' on week and day if necessary
fetalage = weeks + " week" + (weeks > 1 ? "s" : "") + ", " + days + " days";
pregform.fetalage.value = fetalage;

return false; // form should never submit, returns false
}