function isValidDate(dateStr) {
var datePat = /^(\d{1,2})(\/|-)(\d{1,2})\2(\d{4})$/; // requires 4 digit year

var matchArray = dateStr.match(datePat); // is the format ok?
if (matchArray == null) {
alert("Data não está em um formato válido.")
return false;
}
day = matchArray[1]; // parse date into variables
month = matchArray[3];
year = matchArray[4];
if (month < 1 || month > 12) { // check month range
alert("Mês deve ser entre 1 e 12.");
return false;
}
if (day < 1 || day > 31) {
alert("Dia deve situar - se entre 1 e 31.");
return false;
}
if ((month==4 || month==6 || month==9 || month==11) && day==31) {
alert("Mês "+month+" não tem 31 dias!")
return false;
}
if (month == 2) { // check for february 29th
var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
if (day>29 || (day==29 && !isleap)) {
return false;
   }
}
return true;
}

function dispDate(dateObj) {
month = dateObj.getMonth()+1;
month = (month < 10) ? "0" + month : month;

day   = dateObj.getDate();
day = (day < 10) ? "0" + day : day;

year  = dateObj.getYear();
if (year < 2000) year += 1900;

return (day + "/" + month + "/" + year);
}

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 menstrual date
//Original expected mm/dd/yyyy, need to convert
//menstrualinput = new Date(pregform.menstrual.value);
var arr_date = pregform.menstrual.value.split('/');
menstrualinput = new Date();
menstrualinput.setDate(arr_date[0]);	// Day of month
menstrualinput.setMonth(arr_date[1]-1);	// Month
menstrualinput.setFullYear(arr_date[2]);// Year
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 + " semana" + (weeks > 1 ? "s" : "") + ", " + days + " dias";
pregform.fetalage.value = fetalage;

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